Licht MFC-202/P User manual

Parallelism Controller
model MFC-202/P
Technical Manual
Licht

Rev. A2 (30–05–12) MFC-202/P Technical Manual 1
Contents
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
2 Operating principle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3 Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.1 Front panel indication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.2 Manual commands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.3 Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
3.4 Parameter reset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
4 Programmable parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
4.1 MODBUS protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
4.2 DNP3 protocol (option) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
5 Error conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
5.1 Synchronism error . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
5.2 Position deviation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
5.3 Configuration error . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
5.4 Communication error . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
A Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
B Housing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
C Connection diagrams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
D Configuration sheet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
E MODBUS registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

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Rev. A2 (30–05–12) MFC-202/P Technical Manual 2
1 Introduction
The MFC-202/P controller was developed by Licht for the paralellism supervision and
control of 3-phase power transformers and 3-phase groups of monophase transformers.
The MFC-202/P features 10 relays for electromechanic logic, one RS485 interface for
supervision and control and one optional current output for position retransmission.
The parallelism control is implemented according to the master-follower principle, under
which all tap changer positions are kept synchronized. For parallel control to be success-
ful under this scenario, we admit that all involved transformers have identical nominal
currents, number of taps and voltage delta per tap. Each tap changer’s position is read
directly from its potentiometric sensor or indirectly either via a current loop (typically 4-
20 mA) or BCD contacts, according to the client’s specifications. During parallel control,
the Master tap changer’s position is compared to its Followers’, and tap changer pulses
are issued to the Follower tap changers whose positions don’t match their Master’s.
In the MFC-202/P architecture, each controller is responsible for a 3-phase transformer
or a monophase transformer, and is interconnected with other MFC-202/P using a RS485
bus arrangement. MODBUS or DNP3 functionality is provided on a second dedicated
RS485 port, which does not require additional hardware.
Figure 1.1 MFC-202/P controller

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2 Operating principle
General Case
The operation of transformers in parallel can be motivated by expansion, redundancy or
convenience. For it to be practical, the transformers involved must have their secondary
voltages as similar as possible at all times. Otherwise, transformers with lower outputs
become loads to the others, creating circulation currents.
The MFC-202/P is designed for power transformers with on-load tap changers. These
can adjust their tranformation relation as their loads change, guaranteeing adequate reg-
ulation. The Master-Follower principle supposes that the involved transformers have tap
changers with the same number of taps, and that each tap corresponds to the same out-
put voltage. Circulation currents are minimized by operating transformers on identical
positions.
In the Master-Follower principle, a transformer which we denote the Master is chosen as
the reference. The others, denoted Followers, have their positions automatically updated
in order to match the Master. Parallel control is synchronous, because all transformers –
irrespective of being the Master or the Follower – receive simultaneous commands. Trans-
formers can be removed from parallel control if configured as Individual, and completely
ignored if configured as Disabled.
Some exceptional scenarios are detected and treated. These can vary from tap changer
failures (for example, when a Follower transformer doesn’t respond to commands and fails
to match its Master) to configuration errors (for example, configuring a Master without
Followers or Followers without a Master).
Master
Transformer
Position 9
Follower
Transformer
Position 9
Individual
Transformer
Position 5
Figure 2.1 3-phase Transformer Parallelism

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Manual Commands
Transformers configured as Master or Individual can be manually commanded by an
operator. This command may be local (issued on the controller’s keyboard) or remote
(with digital dry contact inputs).
If a Follower transformer fails to respond to tap change commands, the MFC-202/P will
ignore subsequent commands and signal the error condition. In this scenario, the oper-
ator must reconfigure the transformer as Individual and manually manage the system’s
parallelism until a solution can be found.

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3 Operation
3.1 Front panel indication
Under normal operation, the MFC-202/P indicates its channel’s position, operation mode
(Master, Follower, Individual, Disabled) and, if applicable, the raise (↑) or lower (↓)
command indications. Figure 3.1 presents a front panel indication example.
C
P
MULTI FUNCTION CONTROLLER
MFC-202/P
Licht
www.licht-labs.com
Parallelism Controller
Mod. MFC-202/P
Relay 1: Relay 6: Individual
Relay 2: ¯Command Relay 7: Error 1
Relay 3: Manual Relay 8: Error 2
Relay 4: Master Relay 9: Error 3
Relay 5: Follower Relay 10: Unused
Command
Mode: Individual
Pos 01 Addr 00
43 42 45 44 47 46 49 48 51 50 53 52 55 54
56 57 58 59 60 61 62 63 64 65 66 67 68 69
Figure 3.1 Front Panel
In alarm situations, the display alternates between an error message and the channel’s
indication, regardless of the device’s configuration.
3.2 Manual commands
Transformers configured as Master or Individual can be directly commanded by the MFC-
202/P with a manual command. Whenever the transformer is configured as Follower or
Disabled, the command is ignored. Manual commands are only accepted if there’s no
synchronism error between all tap changers.
To perform a manual command, press P, choose the “Manual Command” option, press
Pagain to confirm and then issue a raise or lower command with the ↑or ↓key.
Master
Transformer
↑Position 7 ↑
Follower
Transformer
Position 7
Individual
Transformer
Position 4
Figure 3.2 Raise Command Example (Before)

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Master
Transformer
Position 8
Follower
Transformer
Position 8
Follower
Transformer
Position 4
Figure 3.3 Raise Command Example (After)
3.3 Configuration
The MFC-202/P features 4 keys to access its functions. The procedure to configure any
parameter is as follows:
1. Press the Pkey to enter the parameters menu.
2. Using the ↑and ↓keys, choose the desired parameter.
3. Press Pto confirm the parameter’s selection.
4. Choose the desired value with the ↑and ↓keys.
5. Confirm pressing P.
The configuration sequence can be cancelled at any time by pressing C.
3.4 Parameter reset
The MFC-202/P can be reset to factory settings. This procedure also resets its password
to AAAA. To do so, power on the device while pressing C.

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4 Programmable parameters
The MFC-202/P was developed to provide the user with the greatest possible flexiblity,
such that all supervision and configuration can be executed on-site or remotely through
the existing communication channels.
We define all user-configurable parameters as follows:
Parallelism Mode1
Options:Master,Follower,Individual or Disabled
Description: Selects if the channel operates as Master, Follower, Individual or Disabled.
Number of Positions
Options:2to 50
Description: The on-load tap changer’s number of positions.
Resistance per Position
Opções:3to 20 Ω
Descrição: Resistance in Ωper tap changer position.
Synchronism Error Timeout
Options:10 to 100 s
Description: Interval defined from the instant when failure to follow was detected to
this error’s indication.
Configuration Error Timeout
Options:10 to 100 s
Description: Interval defined from the instant when a configuration failure was detected
to this error’s indication.
Address
Options:0 to 15
Description: Configures this MFC-202/P’s network address. Each tap changer must
have a unique address. A network of MFC-202/Ps can control up to 16 transformers.
Output Current (if any)
Options:0-1,0-5,0-10,0-20,4-20 mA
Description: Refers to the various configurable current loop scales.
This parameter can be only configured using dry contacts.
1

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Relay {7, 8, 9}Configuration
Options: Refer to the table below.
Description: Defines the activation condition for programmable relays 7, 8 e 9.
Activation Condition Occurrence Site Default State MODBUS
Value
Synchronism Error Any MFC-202/P FC 0
FO 1
Configuration Error Any MFC-202/P FC 2
FO 3
Communication Error Any MFC-202/P FC 4
FO 5
Position Deviation Any MFC-202/P FC 6
FO 7
Normal Operation Any MFC-202/P NC 8
NA 9
FC: fail closed
FO: fail open
NC: normally closed
NO: normally open
4.1 MODBUS protocol
Parameter:Baud Rate
Options: 9600, 19200, 38400, 57600, 115200 bps.
Description: baud rate for the RS485 link.
Parameter:Format
Options: 8N1, 8E1, 8O1, 8N2.
Description: symbol transmission format, where:
◦8N1: 8 data bits, no parity, 1 stop bit.
◦8E1: 8 data bits, even parity, 1 stop bit.
◦8O1: 8 data bits, odd parity, 1 stop bit.
◦8N2: 8 data bits, no parity, 2 stop bits.
Parameter:Address
Options: 1 to 247.
Description: MODBUS address for the MFC-202/P.

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4.2 DNP3 protocol (option)
Parameter:Baud Rate
Options: 9600, 19200, 38400, 57600, 115200 bps.
Description: baud rate for the RS-485 link.
Parameter:Format
Options: 8N1, 8E1, 8O1, 8N2.
Description: symbol transmission format, where:
◦8N1: 8 data bits, no parity, 1 stop bit.
◦8E1: 8 data bits, even parity, 1 stop bit.
◦8O1: 8 data bits, odd parity, 1 stop bit.
◦8N2: 8 data bits, no parity, 2 stop bits.
Parameter:Address
Options: 0x0000 to 0xFFEF.
Description: DNP3 outstation address in hexadecimal notation.
Parameter:Application Layer Confirmation
Options: Only when transmitting events or multi-fragment responses, Always.
Description: Selects when the MFC-202/P outstation should request application layer
confirmations.
Parameter:Maximum Inter-Octet Gap
Options: 2 to 100 ms.
Description: The DNP3 specification states that frames should not have inter-octet gaps.
In accordance, the MFC-202/P never inserts inter-octet gaps when transmitting data.
However, we allow the option to tolerate gaps in incoming transmissions. Frames featuring
inter-octet gaps larger than the Maximum Inter-Octet Gap will be quietly dropped.
Parameter:Backoff Delay (Fixed)
Options: 1 to 100 ms.
Description: See description for Backoff Delay (Random).
Parameter:Backoff Delay (Random)
Options: 1 to 100 ms.
Description: The MFC-202/P is designed for multi-drop scenarios where more than
one outstation may transmit over the same line. To handle collision avoidance, a backoff

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scheme is implemented. Before transmitting, the MFC-202/P always waits for the line to
become idle. Once that happens, it waits for Tdelay =Tfixed +Trandom ms, where Tf ixed
is the fixed backoff delay and Trandom is a random value, uniformly distributed between 0
and the random backoff delay parameter. If after Tdelay ms the line is still idle, then the
MFC-202/P begins transmission.
Parameter:Insert Inter-frame Gap
Options: Never, Always.
Description: The DNP3 specification states that no inter-frame gaps are required. How-
ever, some masters have been observed to drop frames when no inter-frame gaps are pro-
vided. This option allows communicating with such non-compliant devices. We discourage
its use, given that the forced inter-frame gap implies a forced backoff-delay.

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5 Error conditions
5.1 Synchronism error
Synchronism errors occur whenever one or more Follower on-load tap changers stop fol-
lowing their Master, despite commands to do so. These may occur between 3-phase
transformers or phases of a 3-phase group of monophase transformers.
Synchronism errors are only set after the user-configurable Syncronism Timeout expires.
Possible causes:
.Connection failure between the raise/lower voltage regulator and the tap changer.
.Tap changer failure, preventing it from receiving and/or executing position changes.
.An Individual transformer is incorrectly configured as Follower.
.The position was manually altered at the tap changer and not through the paral-
lelism controller.
5.2 Position deviation
Position deviations are characterized by readings which shift considerably from their ideal
value. Despite not being large enough to be interpreted as another position altogether,
they suggest failure or imminent failure of the position transducer element, either due to
calibration, tap changer failure or connection problem.
Possible causes:
.EMI (electro-magnetic interference) due to faulty or lack of cable shielding.
.EMI due to failure to ground the cables’ shielding.
.Contact problem.
5.3 Configuration error
Configuration errors may occur in the following scenarios:
.Follower channels without a Master.
.Master channel with no Followers.
.More than one Master.
.Resistance per Position parameter is mismatched between devices.

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5.4 Communication error
Communication errors are characterized by serial (RS485) communication failures be-
tween networked MFC-202/P controllers. Each MFC-202/P is responsible for a given
transformer, and they must exchange position information to correctly operate. Possible
causes for communication errors are:
.More than one MFC-202/P set to the same address.
.Power failure in more than one MFC-202/P.
.Connection failure between networked MFC-202/Ps.
.EMI due to lack of shielding.
.EMI due to failure to ground the cables’ shielding.
.One or more defective MFC-202/P.

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A Specifications
Power Supply Isolated, 80-260 Vac/Vdc.
Power Consumption 5W
Operating Temperature -10 to 70 ◦C(LCD display)
-40 to 70 ◦C(VFD display)
Enclosure Rating IP20
Mounting Options 35 mm DIN Rail
Tap Measurement Inputs 2-wire Potentiometric
Current (e.g.: 4-20 mA)
Voltage (e.g.: 0-10 V)
Number of Positions 2 to 50
Potentiometric Disc Resistance 8 to 1000 Ω
Resistance per Tap 3 to 20 Ω
Dimensions (L x H x D) 160 x 105 x 75 mm
Weight 1.0 kg
DC Scales 0-1, 0-5, 0-10, 0-20, 4-20 mA
Error/Non-linearity (inputs) 0.2% + 0.1% /10 ◦C
Error/Non-linearity (outputs) 0.2% + 0.1% /10 ◦C
Galvanic Isolation
(60 Hz, 1 min.)
Outputs 2.0 kV
Communication 2.0 kV
Communication RS-485 - MODBUS RTU or DNP3
9600, 19200, 38400, 57600, 115200 bps
8N1, 8E1, 8O1, 8N2
Displays 2 lines, 16 characters each (5 mm).
LCD with backlight or VFD.
Relays 10 A@ 250 Vac, 0.5 A@ 125 Vdc
Galvanic Isolation: 2.0 kV, 60 Hz, 1 min.

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B Housing

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C Connection diagrams

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Important considerations
The installation of electronic devices in substations should conform with the recommen-
dations given by recent international standards. The most recent and detailed guide for
installations is IEC 61000-5-2:1997, which was based on decades of laboratory and field
research. We summarize below some of the guidelines contained in IEC 61000-5-2:1997.
For further reading, we recommend the articles and application notes available on our
web site.
a. Shielded cables must be used for connecting potentiometric sensors, current loop
outputs, RS-485 links and the auxiliary supply.
b. Cables must be segregated in trays, ducts or conduits according to their functions.
In particular, power cables must never be routed in the proximity of signal cables,
even if these are shielded. The minimum distances which must be observed are
described in IEC 61000-5-2:1997 and in articles available on-line at this product’s
web page.
c. The electrical continuity of cables, ducts, trays and conduits must be preserved up
to frequencies in the order of MHz, over all their extension, including curves and
junctions. In order to guarantee this continuity, joints and bonds should present
electrical contact along each cable, duct or tray’s transversal section. In particular,
trays should be bonded with seam-welded joints (best), U-brackets with multiple
fixings (ok) and never with wires.
d. Shielded cables should present no gaps in their screens along their lengths. 360◦bond-
ing should be performed instead.
e. Should there be unshielded sections (for example, near terminal block connections),
these should be short as possible.
f. Trays, ducts and conduits must be electrically continuous, and must be grounded
at both ends. In this configuration, trays, ducts and conduits provide shielding
and also perform as parallel earth conductors.
g. Shielded cables should also have their screens bonded at both ends. It is extremely
important that the tray, duct or conduit which contains each cable is also grounded
at both ends, allowing it to perform as a parallel earth conductor. In the absence
of a parallel earth condutor, the cable screens will be exposed to extremely high
currents which will severely compromise their operation.
h. RS-485 pairs must be terminated at both ends by 120 Ωresistors.

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i. RS-485 devices must be connected in a bus topology. No other network topology
(tree, star, ring, etc.) is acceptable.
j. Dry contact inputs (if applicable) must free of potentials.

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D Configuration sheet
Parameter Possible Settings Selected Setting
Device Address 0 to 15
Bus Size 1 to 16
Parallelism Mode Master, Follower, Individual, Disabled
Number of Positions 2 to 50
Resistance per Position 3.0 to 20.0 Ω
Synchronism Error Timeout 10 to 100 s
Configuration Error Timeout 10 to 100 s
Relay 7 Configuration (See section 4)
Relay 8 Configuration (See section 4)
Relay 9 Configuration (See section 4)
Output Current 0-1, 0-5, 0-10, 0-20, 4-20 mA
MODBUS Address 1 to 247
MODBUS Format 8N1, 8E1, 8O1, 8N2
MODBUS Baud Rate 9600, 19200, 38400, 57600, 115200 bps

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E MODBUS registers
Given that each MFC-202/P device only controls a single transformer, network operation
is necessary to implement parallel control. Each MFC-202/P has two RS-485 communi-
cation ports. One is designed for interlinking controllers in a bus topology, and the other
is used for communicating with a SCADA system.
A SCADA system can be connected to any of the networked MFC-202/P controllers.
It may be connected to more than one MFC-202/P, or even to all of them if desired.
Any MFC-202/P knows the states and parameters from all other MFC-202/P devices
connected to it, and is designed to relay this information to a SCADA system.
MODBUS register addresses are 16 bits long. The most significant byte (bits 8-15) must
match the Local Bus Address of the destination MFC-202/P. The least significant byte
(bits 0-7) addresses the actual register in the chosen device. The following pages list the
MODBUS accessible parameters and their associated registers.
As an example, suppose there are 5 interlinked MFC-202/P controllers, with local bus
addresses 0, 1, 2, 3, and 4, and that the SCADA system is connected to controller 3. The
positioned measured by controller N(where Nis one of 0, 1, 2, 3 or 4) may be read by
issuing a MODBUS Read Holding Register (function 0x03) to register N·256 + 200. (We
multiply by 256 to left-shift by 8 bits.) Note that we’re referring to MODBUS registers
in the 0-65535 range. Several server interfaces refer to MODBUS registers in the 1-65536
range. If 1-65536 indexing is desired, add 1 to the computed register values (in our
example, issue a Read Holding Register to address N·256 + 201).
The MFC-202/P implements the Read Holding Register (0x03), Write Single Register
(0x06) and Write Multiple Register (0x10) MODBUS RTU functions. A frame referring
to any other function will be answered with an "unsupported function code" exception.
Frames referring to registers in unreachable or unavailable devices will be answered with
exception Gateway Target Device Failed to Respond (0x0B).