Melitta LOOK User manual

Service Manual
Type MVTU
Definite Time Delayed Relays

Service Manual
Type MVTU
Definite Time Delayed Relays
HANDLING OF ELECTRONIC EQUIPMENT
A person's normal movements can easily generate electrostatic potentials of several thousand volts.
Discharge of these voltages into semiconductor devices when handling electronic circuits can cause
serious damage, which often may not be immediately apparent but the reliability of the circuit will have
been reduced.
The electronic circuits of ALSTOM T&D Protection & Control Ltd products are immune to the relevant levels
of electrostatic discharge when housed in their cases. Do not expose them to the risk of damage by
withdrawing modules unnecessarily.
Each module incorporates the highest practicable protection for its semiconductor devices. However, if it
becomes necessary to withdraw a module, the following precautions should be taken to preserve the high
reliability and long life for which the equipment has been designed and manufactured.
1. Before removing a module, ensure that you are at the same electrostatic potential as the equipment
by touching the case.
2. Handle the module by its front-plate, frame, or edges of the printed circuit board.
Avoid touching the electronic components, printed circuit track or connectors.
3. Do not pass the module to any person without first ensuring that you are both at the same
electrostatic potential. Shaking hands achieves equipotential.
4. Place the module on an antistatic surface, or on a conducting surface which is at the same
potential as yourself.
5. Store or transport the module in a conductive bag.
More information on safe working procedures for all electronic equipment can be found in BS5783 and
IEC 60147-0F.
If you are making measurements on the internal electronic circuitry of an equipment in service, it is
preferable that you are earthed to the case with a conductive wrist strap.
Wrist straps should have a resistance to ground between 500k – 10M ohms. If a wrist strap is not
available, you should maintain regular contact with the case to prevent the build up of static.
Instrumentation which may be used for making measurements should be earthed to the case whenever
possible.
ALSTOM T&D Protection & Control Ltd strongly recommends that detailed investigations on the electronic
circuitry, or modification work, should be carried out in a Special Handling Area such as described in
BS5783 or IEC 60147-0F.

4
TYPES: MVTU 11
Definite Time Delayed Undervoltage Relay
MVTU 12
Definite Time Delayed Overvoltage Relay
MVTU 13
Definite Time Delayed Neutral Displacement Relay
MVTU 18
Definite Time Delayed Neutral Displacement Relay with
Additional Timer
CONTENTS
SAFETY SECTION 6
1. DESCRIPTION OF SETTINGS 10
1.1 Voltage settings 10
1.2 Time settings 10
1.3 Trip indication 10
2. AUXILIARY EQUIPMENT 10
2.1 External series resistors 10
2.2 MVTU 11 Undervoltage and MVTU 12 overvoltage 11
2.3 MVTU 13 Neutral displacement 11
2.4 MVTU 18 Neutral displacement 11
3. INSTALLATION 12
3.1 Precautions 12
3.2 Packing 12
3.3 Inspection 12
3.4 Unpacking 12
3.5 Storage 12
3.6 Siting 12
4. COMMISSIONING TESTS 13
4.1 Inspection and wiring check 13
4.1.1 Electrostatic discharges (ESD) 13
4.2 Connection of the MMLG test block 13
4.3 Earthing 13
4.4 Insulation check 13
4.5 Functional testing 14
4.5.1 DC auxiliary supply check 14
4.5.2 Test block type MMLG 14
4.5.3 Isolation of VT circuit 14
4.5.4 Voltage setting check 15
4.5.5 Timer setting check 18
4.5.6 Final setting checks 19
4.5.7 Trip indicator and contact check 19
4.5.8 Final checks 19

5
5. MAINTENANCE 20
5.1 Visual inspection 20
5.2 Functional checks 20
6. PROBLEM ANALYSIS 20
6.1 Test equipment required for fault finding 20
6.2 General procedure and precautions 21
6.3 Inspection – removal of module from case 21
6.4 Connections for MVTU 11, MVTU 12 and MVTU 13 21
6.5 Checking voltage supplies to module 22
6.6 Printed circuit board tests 22
6.6.1 Monitoring of the voltage across relay coil 22
6.6.2 Measurement of the dc operating currents of the modules 22
6.6.3 Measurement of the ac operating currents of the modules 26
6.7 Calibration information 26
6.8 Repair and replacements 26
6.9 Repair of trip indicator on MVTU 11, MVTU 12 and MVTU 13 relays 26
6.10 Repair and replacement of miniature pcb mounted relay and flag mechanism
(where fitted) 26
6.10.1 Setting up procedure for the flag assembly. 27
6.10.2 Flag replacement parts 28
6.11 Replacements parts – ordering information 28
7 COMMISSIONING TEST RECORD 33
REPAIR FORM 35

6
SAFETY SECTION
This Safety Section should be read before commencing any work on the equipment.
Health and safety
The information in the Safety Section of the product documentation is intended to
ensure that products are properly installed and handled in order to maintain them in
a safe condition. It is assumed that everyone who will be associated with the
equipment will be familiar with the contents of the Safety Section.
Explanation of symbols and labels
The meaning of symbols and labels which may be used on the equipment or in the
product documentation, is given below.
Caution: refer to product documentation Caution: risk of electric shock
Protective/safety *earth terminal
Functional *earth terminal.
Note: this symbol may also be used for a protective/
safety earth terminal if that terminal is part of a
terminal block or sub-assembly eg. power supply.
*Note: The term earth used throughout the product documentation is the direct
equivalent of the North American term ground.
Installing, Commissioning and Servicing
Equipment connections
Personnel undertaking installation, commissioning or servicing work on this
equipment should be aware of the correct working procedures to ensure safety.
The product documentation should be consulted before installing, commissioning or
servicing the equipment.
Terminals exposed during installation, commissioning and maintenance may present
a hazardous voltage unless the equipment is electrically isolated.
If there is unlocked access to the rear of the equipment, care should be taken by all
personnel to avoid electric shock or energy hazards.
Voltage and current connections should be made using insulated crimp terminations
to ensure that terminal block insulation requirements are maintained for safety. To
ensure that wires are correctly terminated, the correct crimp terminal and tool for the
wire size should be used.

7
Before energising the equipment it must be earthed using the protective earth
terminal, or the appropriate termination of the supply plug in the case of plug
connected equipment. Omitting or disconnecting the equipment earth may cause a
safety hazard.
The recommended minimum earth wire size is 2.5 mm2, unless otherwise stated in
the technical data section of the product documentation.
Before energising the equipment, the following should be checked:
Voltage rating and polarity;
CT circuit rating and integrity of connections;
Protective fuse rating;
Integrity of earth connection (
where applicable )
Equipment operating conditions
The equipment should be operated within the specified electrical and environmental
limits.
Current transformer circuits
Do not open the secondary circuit of a live CT since the high voltage produced
may be lethal to personnel and could damage insulation.
External resistors
Where external resistors are fitted to relays, these may present a risk of electric shock
or burns, if touched.
Battery replacement
Where internal batteries are fitted they should be replaced with the recommended
type and be installed with the correct polarity, to avoid possible damage to the
equipment.
Insulation and dielectric strength testing
Insulation testing may leave capacitors charged up to a hazardous voltage. At the
end of each part of the test, the voltage should be gradually reduced to zero, to
discharge capacitors, before the test leads are disconnected.
Insertion of modules and pcb cards
These must not be inserted into or withdrawn from equipment whilst it is energised,
since this may result in damage.
Fibre optic communication
Where fibre optic communication devices are fitted, these should not be viewed
directly. Optical power meters should be used to determine the operation or signal
level of the device.

8
Older Products
Electrical adjustments
Equipments which require direct physical adjustments to their operating mechanism to
change current or voltage settings, should have the electrical power removed before
making the change, to avoid any risk of electric shock.
Mechanical adjustments
The electrical power to the relay contacts should be removed before checking any
mechanical settings, to avoid any risk of electric shock.
Draw out case relays
Removal of the cover on equipment incorporating electromechanical operating
elements, may expose hazardous live parts such as relay contacts.
Insertion and withdrawal of extender cards
When using an extender card, this should not be inserted or withdrawn from the
equipment whilst it is energised. This is to avoid possible shock or damage hazards.
Hazardous live voltages may be accessible on the extender card.
Insertion and withdrawal of heavy current test plugs
When using a heavy current test plug, CT shorting links must be in place before
insertion or removal, to avoid potentially lethal voltages.
Decommissioning and Disposal
Decommissioning: The auxiliary supply circuit in the relay may include capacitors
across the supply or to earth. To avoid electric shock or energy
hazards, after completely isolating the supplies to the relay
(both poles of any dc supply), the capacitors should be safely
discharged via the external terminals prior to decommissioning.
Disposal: It is recommended that incineration and disposal to water
courses is avoided. The product should be disposed of in a safe
manner. Any products containing batteries should have them
removed before disposal, taking precautions to avoid short
circuits. Particular regulations within the country of operation,
may apply to the disposal of lithium batteries.

9
Technical Specifications
Protective fuse rating
The recommended maximum rating of the external protective fuse for this equipment
is 16A, Red Spot type or equivalent, unless otherwise stated in the technical data
section of the product documentation.
Insulation class: IEC 61010-1: 1990/A2: 1995 This equipment requires a
Class I protective (safety) earth
EN 61010-1: 1993/A2: 1995 connection to ensure user
Class I safety.
Installation IEC 61010-1: 1990/A2: 1995 Distribution level, fixed
Category Category III installation. Equipment in
(Overvoltage): EN 61010-1: 1993/A2: 1995 this category is qualification
Category III tested at 5kV peak, 1.2/50µs,
500Ω, 0.5J, between all supply
circuits and earth and also
between independent circuits.
Environment: IEC 61010-1: 1990/A2: 1995 Compliance is demonstrated by
Pollution degree 2 reference to generic safety
EN 61010-1: 1993/A2: 1995 standards.
Pollution degree 2
Product safety: 73/23/EEC Compliance with the European
Commission Low Voltage
Directive.
EN 61010-1: 1993/A2: 1995 Compliance is demonstrated
EN 60950: 1992/A11:1997 by reference to generic safety
standards.

10
Section 1. DESCRIPTION OF SETTINGS
1.1 Voltage settings
The setting voltage is determined by the positions of the six dual-in-line switches.
The sum of all the voltages shown by each respective switch position and the constant
value gives the required setting voltage. For example, an MVTU 11 with the switches
set to the position shown corresponds to a setting of 32 + 26 = 58V ac.
1 ––> 0
Voltage 2 ––> 0 Vs = (32 +∑)
setting 2 <–– 0 = 32 + 2 + 8 + 16
switches 2 ––> 0 = 58V
8 <–– 0
16 <–– 0
For other versions the setting method is identical. Refer to the nameplate on each
individual relay.
1.2 Time settings
The time setting is selected between 0.1 and 9.9 seconds by means of the
thumbwheel switches.
1.3 Trip indication
Earlier relays were fitted with hand reset mechanical flag indicators, later relays
being fitted with non-volatile hand reset LED trip indicators.
Section 2. AUXILIARY EQUIPMENT
2.1 External series resistors
The following dropper resistors pre-mounted on an external assembly, marked with
the relay serial number, are supplied with each relay when required. The part
numbers of the assemblies are listed below together with the resistor values.
The 66kΩexternal resistor, Rext 2, required only on the 380/440V versions, is made
up of two 15kΩand two 18kΩwirewound resistors, all connected in series.
The 380/440V versions are initially calibrated with this external resistor assembly
and if the assembly or any of the resistors on it are changed, the relay must be
recalibrated.

11
2.2 MVTU 11 Undervoltage and MVTU 12 overvoltage
Relay ac Relay dc Resistor assembly Dropper resistor values fitted:
rating (V) rating (V) part number
50/60Hz dc series ac series
resistor (ohm) resistors (ohm)
Rext 1 Rext 2
57/70 30/34 None required — —
100/120
220/250 30/34 ZE0103 020 — 66k
380/440
57/70 48/54 FJ0340 007 220R —
100/120
220/250 48/54 ZE0103 021 220R 66k
380/440
57/70 110/125 FJ0340 001 1k0 —
100/120
220/250 110/125 ZE0103 022 1k0 66k
380/440
57/70 220/250 ZE0103 018 2 x 4k7
100/120 (in parallel) —
220/250 220/250 ZE0103 023 2 x 4k7
380/440 (in parallel) 66k
2.3 MVTU 13 Neutral displacement
Relay ac Relay dc Resistor assembly Dropper resistor fitted:
rating (V) rating (V) part number
50/60Hz dc series ac series
resistor (ohm) resistors (ohm)
Rext 1 Rext 2
57/120 30/34 None required — —
57/120 48/54 FJ0340 007 220R —
57/120 110/125 FJ0340 001 1k0 —
57/120 220/250 ZE0103 018 2 x 4k7
(in parallel) —
2.4 MVTU 18 Neutral displacement
The MVTU 18 does not require external dropper resistors.

12
Section 3. INSTALLATION
3.1 Precautions
Protective relays, although generally of robust construction, require careful treatment
prior to installation and a wise selection of site. By observing a few simple rules the
possibility of premature failure is eliminated and a high degree of performance can
be expected.
3.2 Packing
The relays are either despatched individually or as part of a panel/rack mounted
assembly, in cartons specifically designed to protect them from damage.
3.3 Inspection
Relays should be examined immediately they are received to ensure that no damage
has been sustained in transit. If damage due to rough handling is evident, a claim
should be made to the transport company concerned immediately, and the nearest
ALSTOM T&D Protection & Control representative should be promptly notified.
Relays which are supplied unmounted and not intended for immediate installation
should be returned to their protective polythene bags.
3.4 Unpacking
Care must be taken when unpacking and installing the relays so that none of the
parts is damaged or their settings altered; they should only be handled by skilled
persons.
Relays should be examined for any wedges, clamps or rubber bands necessary to
secure moving parts to prevent damage during transit and these should be removed
after installation and before commissioning.
Relays which have been removed from their cases should not be left in situations
where they are exposed to dust or damp. This particularly applies to installations
which are being carried out at the same time as constructional work.
3.5 Storage
If relays are not installed immediately upon receipt they should be stored in a place
free from dust and moisture in their original cartons and where de-humidifier bags
have been included in the packing they should be retained. The action of the de-
humidifier crystals will be impaired if the bag has been exposed to humid conditions
and may be restored by gently heating the bag for about an hour, prior to replacing
it in the carton.
Dust which collects on a carton may, on subsequent unpacking, find its way into the
relay; in damp conditions the carton and packing may become impregnated with
moisture and the de-humidifying agent will lose its efficiency.
Storage temperature –25 to +70°C.
3.6 Siting
The installation should be clean, dry and reasonably free from dust and excessive
vibration. The site should preferably be well illuminated to facilitate inspection.
An outline diagram is normally supplied showing panel cut-outs and hole centres.
For individually mounted MVTU relays these dimensions will also be found in
Publication R6041.

13
Section 4. COMMISSIONING TESTS
Note: Earlier relays were fitted with hand reset mechanical flag indicators, later
relays being fitted with a non-volatile hand reset LED trip indicator.
CAUTION:
If a flag indicator is fitted, damage is likely to be incurred if the flag indicator/
armature assembly of a miniature relay is actuated manually with a screwdriver/
probe. Flags should always be reset with the cover in position by the mechanism
provided.
4.1 Inspection and wiring check
Carefully examine the module and case to see that no damage has occurred during
transit. Check that the relay serial number on the module, case, cover and resistor
assembly (when an assembly is required) are identical and that the model number
and rating information are correct.
Check that the external wiring is correct to the relevant relay diagram or scheme
diagram. The relay diagram number appears inside the case. Particular attention
should be paid to the wiring of the external resistors Rext 1 and Rext 2 to the relay (if
required on scheme).
4.1.1 Electrostatic discharges (ESD)
The relay uses components which are sensitive to electrostatic discharges.When
handling the module, care should be taken to avoid contact with components and
electrical connections. When removed from the case for storage, the module should
be placed in an electrically conducting anti-static bag. See full recommendations
inside the front cover of this manual.
4.2 Connection of the MMLG test block
If a test block MMLG is provided, the connections should be checked to the scheme
diagram, particularly that the supply connections are to the live side of the test block
(coloured orange) – the odd numbered terminals. The auxiliary supply voltage to the
scheme should be routed via the test block terminals 13 and 15. To facilitate ease of
wiring the MMLG should be located at the right hand side of the assembly.
4.3 Earthing
Ensure that the case earthing connection above the rear terminal block is used to
connect the relay to the local earth bar.
4.4 Insulation check
The relay and its associated wiring, may be insulation tested between:
– all electrically isolated circuits.
– all circuits and earth.
An electronic or brushless insulation tester should be used, having a dc voltage not
exceeding 1kV. Accessible terminals of the same circuit should first be strapped
together. Deliberate circuit earthing links, removed for the tests must subsequently be
replaced.

14
4.5 Functional testing
Equipment required (all versions):
Variac transformer
DC voltmeter to check nominal dc volts
AC voltmeter to cover setting range
Resistance meter
AC ammeter 0-10mA
One double pole switch
One electronic timer
MVTU 11 and MVTU 12 380/440V versions only:
Step-up transformer to cover setting range of 380/440V relay
MVTU 13 and MVTU 18:
One 6W 50kΩwirewound resistor
Note: Measuring accuracy depends on the accuracy of the instruments used.
4.5.1 DC auxiliary supply check
Ensure that the correct series dropping resistor(s) are fitted if required. Remove the
relay from its case and check that the incoming dc supply at the relay case terminal
13(+ve) and 14(–ve) is within the range specified below:
Rated dc voltage (V) DC operative range (V)
30/34 24 – 37.5
48/54 37.5 – 66
110/125 87.5 – 150
220/250 175 – 300
4.5.2 Test block type MMLG
If a test block is included in the scheme, it may also be associated with protection CT
circuits. It is important that the sockets in the type MMLB01 test plug, which
correspond to the current transformer secondary windings, are LINKED BEFORE THE
TEST PLUG IS INSERTED INTO THE TEST BLOCK
DANGER: DO NOT OPEN CIRCUIT THE SECONDARY CIRCUIT OF A
CURRENT TRANSFORMER SINCE THE HIGH VOLTAGE
PRODUCED MAY BE LETHAL AND COULD DAMAGE
INSULATION.
The test plug isolates terminals 13 & 14, removing the dc positive, making it
necessary to add a link between these terminals on the test plug to restore the
auxiliary supply to the relay.
4.5.3 Isolation of VT circuit
Before any secondary injection tests are carried out, the voltage transformer supply to
the relay should be isolated by means of the panel links or connecting blocks.

15
4.5.4 Voltage setting check
The pick-up and drop-off voltages of the relay should be measured with the timer set
to 0.1s and with the voltage setting switches set to each of the positions shown in the
table below.
1 = switch closed (left hand position)
0 = switch open (right hand position)
Table 1
Switch position Pick-up voltage (VRMS)
MVTU 11 MVTU 11 MVTU 11 MVTU 11 MVTU 12 MVTU 12 MVTU 12 MVTU 12 MVTU 13/18
Switch 1 2 3 4 5 6 57/70V 100/120V 220/250 380/440V 57/70V 100/120V 220/250 380/440V 57/120V
Test 1 0 0 0 0 0 0 32 62 135 210 60 105 230 400 5
Test 2 1 0 0 0 0 0 33 63.5 138 216 61.5 107.5 235 410 6
Test 3 0 1 0 0 0 0 34 65 141 222 63 110 240 420 7
Test 4 0 0 1 0 0 0 34 65 141 222 63 110 240 420 7
Test 5 0 0 0 1 0 0 34 65 141 222 63 110 240 420 7
Test 6 0 0 0 0 1 0 40 74 159 258 72 125 270 480 13
Text 7 1 1 1 1 1 1 63 108.5 228 396 106.5 182.5 385 710 36
When the switches have been set for each test, the cover should be replaced to
ensure that the trip indicator is always reset with the cover reset mechanism (where
applicable).
The relays should be connected as shown in the circuit diagrams, Figures 1, 2 and 3.
Figure 1 Test circuit for MVTU 13, 18 and for 57/70V, 110/120V versions of MVTU 11
and MVTU 12
27
28
1
3
5
V
Start
timer
SW1
Test resistor
for MVTU 13
Stop
timer

16
Figure 2 Test circuit for the 220/250V and the 380/440V versions of MVTU 11 and
MVTU 12
Figure 3 Test circuit for 380/440V version of MVTU 11 and MVTU 12 when no
step-up transformer is available
MVTU 11 undervoltage relay
See Figure 1 for the test circuits for the 57/70V and 100/120V versions and Figure
2 for the 220/250V and the 380/440V versions.
If the 380/440V version is being commissioned a step-up transformer is needed to
allow the calibration of the settings to be checked.
The ac input voltage should be increased to a value above the setting value and the
trip indicator reset. Slowly decrease the input voltage until the relay picks up (when
the trip indicator operates). Record the pick-up value.
Slowly increase the voltage, checking to see when the trip indicator can be reset.
This is the drop-off value and should be recorded.
Alternatively, the pick-up and drop-off values can be determined using an ohmmeter
connected across the contacts.
27
28
1
3
5
V
Start
timer
SW1 Stop
timer
REXT2
Step-up
Transformer
27
28
1
3
5
V
Start
timer
SW1 Stop
timer
A

17
Repeat the test for each of the settings shown in Table 1.
The allowable errors on the voltage settings are ±2% on the lowest setting and ±4%
on all other settings (no allowance has been made for instrument errors).
The drop-off value should be within 5% of the pick-up value.
MVTU 12 overvoltage relay
See Figure 1 for the test circuits for the 57/70V and 100/120V versions and Figure
2 for the 220/250V and the 380/440V versions.
If the 380/440V version is being commissioned, a step-up transformer is needed to
allow the calibration of the settings to be checked.
Check that the trip indicator is reset and slowly increase the ac voltage until the trip
indicator operates. Record the pick-up value. Slowly lower the voltage to see when
the trip indicator can be reset. This is the drop-off value and should be recorded.
The allowable errors on the voltage settings are ±2% on the lowest setting and ±4%
on all other settings (no allowance has been made for instrument errors).
The drop-off value should be within 5% of the pick-up value.
Alternative test method for 380/440V versions of MVTU 11 and MVTU 12
This method should be used only when no step-up transformer is available.
See Figure 3 for the test circuit.
Firstly, accurately measure the resistance of the dropper resistor assembly (Rext 2).
With the relay on the lowest setting and the dropper resistor (Rext 2) removed from
the circuit, measure the pick-up voltage directly at the relay terminals 27 and 28 and
the ac current into the relay at the pick-up voltage. Use the following formula to
calculate the effective pick-up voltage:
Veff = VM + IMRM
where Veff = effective pick-up voltage
VM= measured pick-up voltage with Rext 2 out of circuit
IM= the measured pick-up current with Rext 2 out of circuit
RM= measured resistance of Rext 2
The drop-off voltage can be found in the same way.
The pick-up voltage should be within ±2% of the lowest setting voltage.
No allowance has been made for instrument errors.
This test has checked the calibration point of the relay. The other relay settings need
only be checked to see that they are functioning. Refer to Tests 2 – 7 in Table 1 for
the appropriate switch positions.
With the dropper resistors (Rext 2) still out of circuit, monitor the voltage at the relay
terminals 27 and 28 for the MVTU 12. Slowly increase the voltage until the relay
picks up and record the pick-up value. Slowly lower the voltage until the relay drops
off and record the drop-off value. For the MVTU 11, slowly decrease the voltage to
record the pick-up value and then increase the voltage to record the drop off value.
On the MVTU 12, if the pick-up voltage at the 400V setting is Z, the measured pick-
up voltages at the other settings should be higher than the 400V setting by the
amounts shown. A similar method is adopted for the MVTU 11.

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Setting voltage Pick-up voltage at relay input
Test number (V) terminals (27 & 28) (V)
MVTU 11 MVTU 12 MVTU 11 MVTU 12
1 210 400 Z Z
2 216 410 Z + 1 ±1 Z + 2 ±1
3, 4, 5 222 420 Z + 2 ±1 Z + 4 ±1
6 258 480 Z + 10 ±2 Z + 17 ±2
7 396 710 Z + 39 ±3 Z + 66 ±4
The drop-off voltages should be within 5% of the pick-up values.
MVTU 13 and MVTU 18 neutral displacement relays
A series dropper resistor of approximately 50kΩshould be inserted in series with the
input terminals 27 and 28 to allow sufficient sensitivity in the setting range when
using a 0 – 240V variac supply, see Figure 1 for the test circuit.
Check that the trip indicator is reset and slowly increase the ac input voltage until the
trip indicator operates. Record the pick-up value.
Slowly lower the voltage, checking to see when the trip indicator can be reset.
This is the drop-off value and should be recorded.
Alternatively, the pick-up and drop-off states can be determined by connecting an
ohmmeter across the contacts.
Repeat the test for each of the settings shown in Table 1.
The allowable errors on the voltage settings are ±2% on the lowest setting and ±4%
on all other settings.
(No allowance has been made for instrument errors.)
The drop-off value should be within 5% of the pick-up value.
4.5.5 Timer setting check
It is recommended that all MVTU relays are tested on the following timer settings:
1.1, 2.2, 3.3, 4.4, 5.5, 6.6, 7.7, 8.8, 9.9 seconds. The circuit diagrams for these
tests are shown in Figures 1, 2 and 3.
The applied voltage levels should be greater than 10% above and 10% below any
convenient voltage setting.
MVTU 11 – undervoltage
Remove the ac supply from 10% above the voltage setting to zero volts,
simultaneously starting the timer. The timer stop contacts should be connected to the
relay output contacts. The allowable errors in the timer settings are ±3% or 70ms
whichever is the greater.
MVTU 12 – overvoltage and MVTU 13 – neutral displacement
Apply the ac supply from zero to 10% above the voltage setting, simultaneously
starting the timer. The timer stop contacts should be connected to the relay output
contacts. The allowable errors in the timer settings are ±3% or 70ms whichever is
the greater.

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MVTU 18 – neutral displacement
Time delay t1is checked as for MVTU 13
Time delay t2is checked by connecting the timer as shown in Figure 4 and repeating
the tests as for time delay t1.
Figure 4 Test circuit for MVTU 18 relay
4.5.6 Final setting checks
Adjust the voltage setting to its functional setting and measure the pick-up and drop-
off values as already mentioned. Check that they are within the stated tolerance.
With the final voltage setting and the functional timer setting selected, measure the
operating times when a voltage ≥1.1x the setting voltage is applied (≤0.9x for MVTU
11). Check that this is within the stated tolerance.
4.5.7 Trip indicator and contact check
Check that the trip indicator and reset facility operate. Also check that the contacts
operate by carrying out continuity checks.
4.5.8 Final checks
Operate the relay with the trip and alarm links restored to ensure that the trip and
alarm circuits are energised according to the relevant schematic diagram.
Remove all test leads, test switches, temporary shorting leads etc.
Replace any links that have been removed to facilitate testing.
If a test plug (MMLB) and test block (MMLG) have been used, remove the test plug.
CAUTION:
Replace the test block cover to put the protection in service.
27
28
1
3
5
V
Start
timer T1
SW1
Stop timer
T1
2
4
6
Start
timer
T2
7
9
1
Stop timer
T2

20
Section 5. MAINTENANCE
Periodic maintenance is not necessary. However, periodic inspection and test is
recommended.
5.1 Visual inspection
Isolate all supplies and withdraw the module from the case using the two black
handles on the relay. Inspect the printed circuit board for any sign of loose
components or connections.
Note that, where fitted, flag mechanisms should not be disturbed unless found to be
operating incorrectly during the routine function tests.
Your attention is drawn to the fact that the relay can be damaged by electrostatic
discharges. The pcb should not be touched unless precautions have been taken.
5.2 Functional checks
Periodic function tests should be carried out using the test procedures shown in the
commissioning section.
The operation of the trip indicator and the reset facility should be checked during
these functional tests.
Section 6. PROBLEM ANALYSIS
These instructions enable a fault to be localised to sub-assembly level. Fault finding to
component level is not recommended. The main reasons for this are as follows:
– Fault finding on printed circuit boards requires the use of specialised knowledge
and equipment.
– Components used in manufacture are subject to strict quality control and in
certain cases selected for particular characteristics. Complementary metal oxide
silicon (CMOS) components are used, which require extremely careful handling.
– Damage can be caused to the printed circuit track unless extreme care is used in
the replacement of components.
– Replacement of some components will necessitate recalibration of the relay.
– The printed circuit boards are covered with a protective coating of polycoat
which makes access to tracks and components very difficult.
6.1 Test equipment required for fault finding
Equipment required for fault finding is minimal and consists of the following:
– Digital multimeter with ranges of 0 – 1000V ac/dc and 0 – 1A ac/dc
– DC voltage supply 30V 0.5A
– AC voltage source 0 – 500V 50Hz at 10mA
– Oscilloscope (optional)
– Relay tool kit