Woodward WIP1 User manual

WIP1 –Self Powered Time Overcurrent Relay
Manual WIP1 (Revision J)
Released

Manual WIP1 Woodward
DOK-TD-WIP1E Rev. J 2
Woodward reserves the right to update any portion of this publication at any time. Information provided by Woodward
is believed to be correct and reliable. However, no responsibility is assumed by Woodward unless otherwise expressly
undertaken.
© Woodward 1994-2017
Released

Manual WIP1 Woodward
DOK-TD-WIP1E Rev. J 3
Contents
1. Comments on the Manual ........................................................................................5
1.1 Information Concerning Liability and Warranty.................................................................................. 5
1.2 IMPORTANT DEFINITIONS.............................................................................................................. 6
2. General ......................................................................................................................7
3. Characteristics and Features...................................................................................8
4. Design........................................................................................................................9
4.1 Connections....................................................................................................................................... 9
4.1.1 Connecting the Serial Interface ................................................................................................... 13
4.1.2 Current Transformer Inputs ......................................................................................................... 14
4.1.3 Control Inputs............................................................................................................................... 14
4.1.4 Operation Outputs ....................................................................................................................... 15
4.1.5 Trip Indication .............................................................................................................................. 16
4.1.6 Serial Interface............................................................................................................................. 16
5. Working Principle ...................................................................................................17
5.1 Current Transformer Inputs ............................................................................................................. 17
5.2 Digital Circuits.................................................................................................................................. 17
5.3 Relay Clock for Timestamps............................................................................................................ 17
5.4 Operating Modes ............................................................................................................................. 18
5.4.1 Phase Current ≥ 0.5 A (CT-Powered Mode) ............................................................................... 18
5.4.2 Phase Current < approx. 0.35 A (Offline Mode).......................................................................... 18
5.4.3 Dual Power Option for WIP1-2 and WIP1-3................................................................................ 18
5.5 Indicating and Operating Elements ................................................................................................. 19
5.5.1 Front Plate ................................................................................................................................... 19
5.5.2 Display......................................................................................................................................... 19
5.5.3 LED.............................................................................................................................................. 19
5.6 Function Push Buttons..................................................................................................................... 19
5.7Requirements for the Main C.T.s..................................................................................................... 20
5.7.1 Determining the Maximum Coil Resistance................................................................................. 20
5.7.2 Characteristics of the Current Transformers ............................................................................... 21
5.7.3 Overloading of the WIP1.............................................................................................................. 23
5.7.4 Dimensioning Example................................................................................................................ 24
6. Operations and Settings ........................................................................................26
6.1 Function of Push Buttons................................................................................................................. 27
6.1.1 Measuring Value and Fault Indication ......................................................................................... 27
6.1.2 Display......................................................................................................................................... 28
6.1.3 Setting Procedure........................................................................................................................ 28
6.1.4Parameter setting by using the password ................................................................................... 28
6.2 Display of Measuring Values........................................................................................................... 29
6.3 Displaying the Pickup Phase........................................................................................................... 30
6.4 Display of Tripping Values............................................................................................................... 30
6.5 Protection parameters ..................................................................................................................... 32
6.5.1 Pickup Value for Phase Overcurrent Element............................................................................. 32
6.5.2 Time Current Characteristics for Phase Overcurrent Element.................................................... 32
6.5.3 Trip Delay or Time Multiplier for Phase Overcurrent Element..................................................... 32
6.5.4 Reset Mode for Inverse Time Tripping Characteristics for Phase Overcurrent Element ............ 33
6.5.5 Minimal Time................................................................................................................................ 33
6.5.6 Current setting for High Set Element........................................................................................... 33
6.5.7 Trip Delay for High Set Element.................................................................................................. 33
6.5.8 Pickup Value for Earth Fault Current Element............................................................................. 34
6.5.9 Tripping Characteristic for Earth Fault Current Element.............................................................. 34
6.5.10 Trip delay or Time Multiplier for Earth Fault Overcurrent Element.......................................... 34
6.5.11 Reset Mode for Normal Inverse Time Tripping Characteristics for Earth Fault Element ........ 34
6.5.12 Minimum Tripping Time (Earth Fault Element)........................................................................ 34
6.5.13 Current Setting for Earth Fault High Set Element.................................................................... 34
6.5.14 Trip Delay for Earth Fault High Set Element ........................................................................... 34
6.6 System Parameters ......................................................................................................................... 35
Released

Manual WIP1 Woodward
DOK-TD-WIP1E Rev. J 4
6.6.1 Selection of the Language........................................................................................................... 35
6.6.2 Password Programming .............................................................................................................. 35
6.6.3 Date Setting................................................................................................................................. 36
6.6.4 Time Setting................................................................................................................................. 36
6.6.5 Rated Frequency Setting............................................................................................................. 36
6.6.6 Setting of the Communication Slave Address (only WIP1-3)...................................................... 36
6.6.7 Baud Rate Setting (only WI1-3)................................................................................................... 36
6.6.8 Setting of Parity (only WIP1-3) .................................................................................................... 37
6.6.9 Indication of the Software Version............................................................................................... 37
6.7 Tripping Method/Relay Matrix.......................................................................................................... 37
6.7.1 Reset............................................................................................................................................ 37
6.7.2 Tripping method........................................................................................................................... 37
6.7.3 Earth Fault Overcurrent............................................................................................................... 38
6.7.4 Flashing of the Trip-LED.............................................................................................................. 38
6.7.5 Relay matrix (only relay 2)........................................................................................................... 38
6.8 Signal Inputs.................................................................................................................................... 39
6.8.1 Fast Trip....................................................................................................................................... 39
6.8.2 Blocking the Protection Functions ............................................................................................... 39
6.9 Reset................................................................................................................................................ 39
6.10 Clearing the Fault Memory .............................................................................................................. 40
7. Relay Testing and Commissioning .......................................................................41
7.1 Checking the Set Values ................................................................................................................. 41
7.2 Secondary Injection Test ................................................................................................................. 41
7.2.1 Test Equipment............................................................................................................................ 41
7.2.2 Example of Test Circuit................................................................................................................ 42
7.2.3 Checking the Tripping Circuits..................................................................................................... 43
7.2.4 Checking the Input Circuits and Measured Values...................................................................... 45
7.2.5 Checking the Overcurrent Element ............................................................................................. 45
7.2.6 Checking the High Set Element of the Relay .............................................................................. 45
7.2.7 Checking the External Blocking................................................................................................... 46
7.2.8 Checking the Input “Fast Trip” ..................................................................................................... 46
7.2.9 Remote Trip................................................................................................................................. 46
7.2.10 Test of Input „External Reset“.................................................................................................. 46
7.3 Primary Injection Test...................................................................................................................... 46
7.4Benefits from Using the Display Battery.......................................................................................... 47
8. Maintenance............................................................................................................48
8.1 Opening the Front Cover................................................................................................................. 48
8.2 Display Battery................................................................................................................................. 49
8.2.1 Checking the Battery ................................................................................................................... 49
8.2.2 Changing the Battery................................................................................................................... 49
9. Technical Data.........................................................................................................52
9.1 System Data .................................................................................................................................... 54
9.2 Setting Ranges and Steps............................................................................................................... 55
9.3 Inverse Time Tripping Characteristics............................................................................................. 56
9.3.1 Tripping Characteristics............................................................................................................... 58
9.4 Relay Case ...................................................................................................................................... 65
9.5 Flag Indicators ................................................................................................................................. 66
10. FAQ (Frequently Asked Questions) ......................................................................67
11. Order Form..............................................................................................................69
Released

Manual WIP1 Woodward
DOK-TD-WIP1E Rev. J 5
1.Comments on the Manual
This manual explains in general the tasks of device planning, parameter setting, installation, commissioning,
operation and maintenance of the WIP1 device.
The manual serves as working basis for the following user types:
engineers in the protection field,
commissioning engineers,
people dealing with setting, testing and maintenance of protection and control devices,
trained personnel for electrical installations and power stations.
All functions concerning the type code will be defined. Should there be a description of any functions, pa-
rameters or inputs/outputs which do not apply to the device in use, please ignore that information.
All details and references are explained to the best of our knowledge and are based on our experience and
observations.
This manual describes the (optionally) full featured versions of the devices.
All technical information and data included in this manual reflect their state at the time this document was is-
sued. We reserve the right to carry out technical modifications in line with further development without
changing this manual and without previous notice. Hence no claim can be brought based on the information
and descriptions this manual includes.
Text, graphic and formulae do not always apply to the actual delivery scope. The drawings and graphics are
not true to scale. We do not accept any liability for damage and operational failures caused by operating er-
rors or disregarding the directions of this manual.
No part of this manual is allowed to be reproduced or passed on to others in any form, unless Woodward
Kempen GmbH have approved in writing.
This user manual is part of the delivery scope when purchasing the device. In case the device is passed on
(sold) to a third party, the manual has to be handed over as well.
Any repair work carried out on the device requires skilled and competent personnel who need to be well
aware especially of the local safety regulations and have the necessary experience for working on electronic
protection devices and power installations (provided by evidence).
1.1 Information Concerning Liability and Warranty
Woodward Kempen GmbH does not accept any liability for damage resulting from conversions or changes
carried out on the device or planning (projecting) work, parameter setting or adjustment changes done by the
customer.
The warranty expires after a device has been opened by others than Woodward Kempen GmbH specialists.
Warranty and liability conditions stated in Woodward Kempen GmbH General Terms and Conditions are not
supplemented by the above mentioned explanations.
Released

Manual WIP1 Woodward
DOK-TD-WIP1E Rev. J 6
1.2 IMPORTANT DEFINITIONS
The signal definitions shown below serve the safety of life and limb as well as for the appropriate operating
life of the device.
DANGER indicates a hazardous situation which, if not avoided,
will result in death or serious injury.
WARNING indicates a hazardous situation which, if not avoided, can
result in death or serious injury.
CAUTION, used with the safety alert symbol, indicates a hazardous
situation which, if not avoided, can result in minor or moderate injury.
NOTICE is used to address practices not related to personal injury.
CAUTION, without the safety alert symbol, is used to address practices not
related to personal injury.
Woodward Kempen GmbH reserves the right to update any portion of this publication at any time.
Information provided by Woodward Kempen GmbH is believed to be correct and reliable. However,
no responsibility is assumed by Woodward Kempen GmbH unless otherwise expressly undertaken.
© Woodward 2017. All rights reserved.
Released

Manual WIP1 Woodward
DOK-TD-WIP1E Rev. J 7
2.General
The WIP1 is a self-powered time overcurrent relay with multi-characteristics and including earth fault protec-
tion. Definite time and inverse time tripping characteristics can be selected.
Due to its wide setting ranges, the tripping characteristic can be selected to protect a wide variety of different
equipment.
The WIP1 does not require any aux. voltage supply, consequently it can also be used for switchboards with-
out auxiliary power supply. It takes its power supply energy from the C.T. circuits and provides the tripping
pulse energy to the circuit breaker.
The WIP1 is a robust protective device that is designed for a long-time operation with minimum maintenance
efforts even under extreme climate conditions. Our experience with WI Line self-powered protective relays
shows that the MTBF („Mean Time Between Failures“) is approx. 200 years (calculated based on data up to
year 2012), and there are WIP1 relays being in service at our customers’ sites for more than 22 years even
under harsh climate conditions.
Released

Manual WIP1 Woodward
DOK-TD-WIP1E Rev. J 8
3.Characteristics and Features
Auxiliary voltage supply is not required
User-friendly setting procedure with wide setting ranges
Protective Elements will use DFT signals (50/60 Hz Signals) only. Digital filtering of measured quan-
tities by using discrete Fourier analysis to suppress high frequency harmonics and transient DC
components induced by faults or system operations
2.nd harmonics filtering (Inrush)
Two-element overcurrent and short circuit relay
Selectable protection functions between:
- definite time overcurrent and
- inverse time overcurrent
Selectable inverse time characteristics acc. to IEC 255-4:
- normal inverse (type A)
- very inverse (type B)
- extremely inverse (type C)
- special characteristics
Earth fault protection with 2 stages (IE>, IE>>)
Reset mode for inverse time characteristics selectable
High-set overcurrent element with instantaneous or definite time function
Two-stage earth fault supervision with tripping and/or alarm function
Redundant power supply unit for external voltage supply (Option WIP1-2)
Serial interface for connection to SCADA Systems (Option WIP1-3)
Phase and earth current measuring during normal operation
Fault values can be shown on the display.
Fault values are stored within the relay together with a timestamp.
Five fault memories
High-accuracy components and over-rating guarantee precision, reliability and a long
service life
High operating reliability through internal self-supervision (watchdog); internal faults are
indicated by an alarm relay
Remote tripping via external voltage
High-capacity electric pulse output for direct triggering the circuit breaker
Trip indication via external flag indicator with mechanical reset
Two potential free alarm contacts, latched type (bi-stable relay)
Relay with one potential free contact; tripping function selectable
Trip value indication via LCD display, battery-buffered
Compact construction
Insensitive to extreme environmental conditions
In accordance with the specified technical data, it complies with the requirement of
VDE regulation 0435-303, IEC255, VDE 0843
Released

Manual WIP1 Woodward
DOK-TD-WIP1E Rev. J 9
4.Design
4.1 Connections
fast trip
WIP_Z03
signal relay impuls
tripping out
tripping
remote
supply
power
serial interface
RS485
supervision
self trip relay reset
reserve
blocking input
L1 L2 L3
S1
S2
S3
S1
S2
S3
S1
S2
S3
1S1
1S2
2S1
2S2
3S1
3S2
1E1
1E2
32 33 23 24 25 26 27 28 11 12 1 2 1E1 1E2 1S1 2S1 3S1 1S2 2S2 3S2 20 22
A1 A2 J1 P N J2 29 30 31 34 35 36 14 15 16 17
Figure 4.1: Connection example with relay tripping
It is mandatory that the WIP1 is grounded (earthed) via the terminal marked
by “ ”.
All grounding connections must be low-inductance, i. e. as short as
possible, and national standards –if applicable –must be followed.
Released

Manual WIP1 Woodward
DOK-TD-WIP1E Rev. J 10
Figure 4.2: Connection including earth fault detection via Holmgreen connection
Please note: In this circuit we recommend earthing the current
transformers via the relay connection.
*1: If the current transformers have to be earthed directly, the earthing
connection on WIP1 must be removed. Otherwise the measuring
transformer for earth fault measuring is short-circuited.
Released

Manual WIP1 Woodward
DOK-TD-WIP1E Rev. J 11
Figure 4.3: Connection for measuring only phase current
Released

Manual WIP1 Woodward
DOK-TD-WIP1E Rev. J 12
Figure 4.4: Connection including earth fault detection via C.T. cable type
Released

Manual WIP1 Woodward
DOK-TD-WIP1E Rev. J 13
4.1.1 Connecting the Serial Interface
The relays are connected to a PC/laptop via an RS232/RS485-interface converter by using the two-wire
method. Each relay is connected to terminals P and N. The last relay in terms of “hardware”must then be
equipped with terminating resistors. This is done by connecting terminals P with J1 and N with J2.
Figure 4.5: Connection of the serial interface
Released

Manual WIP1 Woodward
DOK-TD-WIP1E Rev. J 14
4.1.2 Current Transformer Inputs
The protection unit WIP1 receives the analog input signals of the phase currents IL1 (1S1 ‑1S2),
IL2 (2S1 ‑2S2) and IL3 (3S1 ‑3S2) for phase current, earth current and negative sequence measuring.
The measured current values are analogously filtered and fed to the analog/digital converter.
4.1.3 Control Inputs
Input remote tripping
The remote tripping input (terminals 20 and 22) enables tripping by an external voltage pulse, e. g. from a
thermal overcurrent tripping device, Buchholz protection or other external trip commands. By bypassing the
measuring circuits, this input (230 V AC max. 5 min) has a direct effect on the trip circuit. The input terminals
are galvanically decoupled from the relay electronics.
Signal inputs
Signal inputs for blocking and protection (terminals 14 and 17) for fast trip (terminals 32 and 33) as well as
external reset (terminals 14 and 15) can be activated by applying an external voltage. (Voltage level: see
“Signal inputs” in Chapter 9.)
Blocking function (terminals 14 and 17):
Single or all trip elements can either be blocked or re-leased.
Fast trip (terminals 32 and 33):
By this function the CB can be tripped instantaneously. There are two different kind of trippings:
Instantaneous means, a trip is initiated as soon as the minimum current is available (lowest power
supply value adjustable).
After activation means, the high-speed tripping function only is activated if one of the phase
currents exceeds the set value.
The fast trip input can be applied for e.g. arcing fault detectors.
Reset
After a trip event the alarm relay is reset and the LED extinguishes when voltage is applied (see also
chapter 6.9 “Reset”. For the voltage level: see “Signal inputs” in Chapter 9).
Released

Manual WIP1 Woodward
DOK-TD-WIP1E Rev. J 15
4.1.4 Operation Outputs
There is the choice of two tripping methods:
Electric pulse output
A trip command is a sequence of power pulses that the WIP1 gives directly to the tripping coil of the CB
(terminals 1 and 2). These pulses are given every 150 ms and repeated until the CB is switched off. (See
also “Electro pulse output circuit” in Chapter “Technical Data”.)
Potential free contacts (relay 1/latching) terminals (23, 24, 28 and 24, 25, 26)
For applications where a higher trip output energy is required, a bi-stable relay with two potential free
changeover contacts is provided in the trip circuit. After the relay has tripped, the contacts remain in trip
position until reset by the <RESET> push button.
Potential free contacts (relay 2) terminals (34, 35, 36)
For applications where a higher trip output energy is required, a relay with one potential free changeover
contact is provided in the trip circuit. This Relay can be assigned to any function (see 6.7 “Tripping
Method/Relay Matrix”).
Example:
When using DC coils it has be observed that the breaking capacity of the output contacts is not unlimited
(see chapter 7).
In case the coil burden is higher than the contact breaking capacity, the following circuit arrangement can be
used:
Figure 4.6: Example
By connecting a trip contact of the WIP1 and an aux. contact of the C.B. in series it is prevented that the
WIP1 contact is arcing so that safe switching off is guaranteed.
Watchdog (Terminals 29, 30, 31):
For continuous supervision of the program flow a “hardware watchdog”is installed. In case of processor
failure, the watchdog is activated after detection of a specific minimal current. The self-supervision relay
is a working current relay.
Released

Manual WIP1 Woodward
DOK-TD-WIP1E Rev. J 16
4.1.5 Trip Indication
The WIP1 is provided with an LED for the optical trip indication. Tripping can additionally be indicated via an
external indicator. Flashing of the LED can be suppressed by parameter setting.
Fault values can be shown on the display, and moreover, the fault values are stored within the relay together
with a timestamp.
4.1.6 Serial Interface
By way of hardware the serial interface is a RS-485 interface. The WIP1-3 relay can alternatively be pro-
vided with either Modbus Protocol or Woodward-Pro Open Data Protocol. For protocol data please see the
Profi-Pack file for Modbus or the Woodward-Pro Open Data Protocol.
Released

Manual WIP1 Woodward
DOK-TD-WIP1E Rev. J 17
5.Working Principle
5.1 Current Transformer Inputs
The alternating currents induced by the main current transformers provide the WIP1's supply energy and
form the measuring value. The measuring currents are galvanically isolated via the input transformers,
decoupled from high-frequency interferences by analog RC-filters and then converted into current
proportional voltages. The noise signals caused by inductive and capacitive coupling are suppressed by an
analog R-C filter circuit. The analog voltage signals are fed to the A/D-converter of the microprocessor and
transformed to digital signals through Sample-and-Hold-circuits. The analog signals are sampled at 50 Hz
(60 Hz) with a sampling frequency of 800 Hz (960 Hz), namely, a sampling rate of 1.25 ms (1.04 ms) for
every measuring quantity. (16 samples per period).
5.2 Digital Circuits
The essential part of the WIP1 is a powerful microcontroller. All of the operations - from the analogue/digital
conversion to the relay trip decision - are carried out by the microcontroller digitally. The relay program is
saved in an EPROM (Electrically-Programmable-Read-Only-Memory). With this program the CPU of the
microcontroller processes the voltages applied at the analogue input circuits and calculates the basic current
harmonics. For this calculation an efficient digital filter, based on the Fourier Transformation (DFT –Discrete
Fourier Transformation) is applied to suppress high frequency harmonics and DC components caused by
fault-induced transients or other system disturbances. The relay setting values for all parameters are saved
in a parameter memory (EEPROM - Electrically Erasable Programmable Read-only Memory) and constantly
compared with the actual current by the microprocessor. If a phase current exceeds the pickup value, an
alarm is given and after the set trip delay has elapsed, the corresponding trip relay is activated. For
continuous supervision of the program flow a “hardware watchdog”is installed. In case of failure, the
watchdog timer resets the microprocessor and gives an alarm signal via the “self-supervision”output relay.
Such a failure is indicated by the following display:
_Internal_Fault__
________________
5.3 Relay Clock for Timestamps
The relay is provided with a buffered clock so that the system time is kept even the power supply is
interrupted. (All protection functions remain fully functional even if the battery is empty or not fitted at all.)
Released

Manual WIP1 Woodward
DOK-TD-WIP1E Rev. J 18
5.4 Operating Modes
5.4.1 Phase Current ≥ 0.5 A (CT-Powered Mode)
The WIP1 is already fully operational –including all protection functions and a permanent display of
measurement values (see 6.2) –as soon as the CT current is ≥ 0.5 A in at least one phase. (This is also the
smallest possible setting for the tripping threshold.) Dual-power (which is an option only for WIP1-2 and
WIP1-3) reduces this even further, see 5.4.3.
Note that some functionality is already available below 0.5 A (for exact data see 9.2). In particular, the
automatic reset has to be mentioned here from the user’s point of view. (See description in Chapter 6.9
“Reset”.)
5.4.2 Phase Current < approx. 0.35 A (Offline Mode)
Without any power supply (if there is no dual-power and the phase current is not sufficient to enter the CT-
powered mode) the WIP1 can be activated by pressing the <DISPLAY ON> button. (The display is then
powered by the display battery.)
The WIP1 normally shows the menu for parameter settings. This allows for configuring the relay
“offline”, i. e. without having it connected to the substation.
However, if the WIP1 had tripped and therefore switched off its power supply via the CTs, then it
shows the Fault Memory menu after pressing the <DISPLAY ON> button.
See Figure 6.1 for an overview of the menu structure.
Note the following for WIP1-1 and WIP1-2/3 without dual-power option:
If the maximum phase current is between approx. 0.35 A and 0.5 A it can
happen that after pressing the <DISPLAY ON> button the WIP1 tries to
enter the CT-Powered Mode although the power supply is not sufficient for
this.
One can recognize this activity by the fact that the display shows nothing
but a “–” character.
In this case entering the offline mode is only possible after the CT current
has been reduced below approx. 0.3 A (e. g. by simply disconnecting
the WIP1).
5.4.3 Dual Power Option for WIP1-2 and WIP1-3
The relay versions WIP1-2 and WIP1-3 offer a dual power option, i. e. the option to connect an additional
external power supply.
The dual power source makes the relay operational independently of the supply via the CTs. Moreover,
there is an extended setting range for the phase overcurrent protection, the lowest possible pickup threshold
is 0.2 A.
The dual-power will make the relay n-1 secure, because the electrical power that the relay requires for
operation is taken either from the dual power source or from the CTs.
Released

Manual WIP1 Woodward
DOK-TD-WIP1E Rev. J 19
5.5 Indicating and Operating Elements
5.5.1 Front Plate
There are the following indicating and operating elements at the front of the relay:
Two-line LC display with 16 characters per line
Push buttons for adjustment and operation
LED for trip indication
5.5.2 Display
All setting and measuring values as well as fault data are shown in the LC display.
5.5.3 LED
The trip status is indicated by the LED at the front. If the relay has tripped, the LED flashes and can be
switched off by pressing any push button. Refer to chapters 6.7.4 and 6.9.
5.6 Function Push Buttons
The following four function push buttons are arranged at the front of the relay:
<SELECT/RESET> “Select”= Selection of function displayed (short pressing of the
push button) “Reset” = Reset of trip functions (long pressing of the
push button, for 3 s)
<+> and <-> Selection of parameters
<ENTER> Storing parameters
<DISPLAY ON> Switching the relay on. If no key is pressed longer than 1 min. the relay
switches off.
The push buttons <SELECT/RESET>, <+>, <-> and <DISPLAY ON> can be activated without removing the
transparent cover by simply using a pin or screw driver.
Figure 5.1: Front plate of WIP1
Released

Manual WIP1 Woodward
DOK-TD-WIP1E Rev. J 20
5.7 Requirements for the Main C.T.s
The advantage of self-powered overcurrent relays is that they do not need any auxiliary power supply. This
results from the fact that the overcurrent relay and the tripping unit receive their energy from the main C.T.s.
The tripping principle of the WIP1 is that the transformer current is driven through the tripping coil in case
tripping takes place. Care must be taken that the current transformer can transmit enough energy at the set
overcurrent pickup value to activate the tripping coil, but does not generate too much energy at high short
circuit currents which would damage the overcurrent relay.
The tripping coil and current transformer have to be determined as follows.
First of all it must be established how much force is required to cause the C.B. to trip. This force must be
converted to electric energy. It can also be established by measurement. This value is very important.
Many coils are defined by way of their rated data such as rated voltage, rated current, internal resistance
and/or permissible on-period. These data do not permit any conclusions regarding the usability of a coil as
the tripping capacity with rated data is usually much higher than is necessary for safe tripping.
5.7.1 Determining the Maximum Coil Resistance
Figure 5.2: Tripping via current transformer I < 12 x In
Figure 5.3: Tripping via self-supply as from 12 x In
Released