This document describes a system for synchronizing and load sharing between two diesel generators (DG1 rated at 500kVA and DG2 rated at 320kVA) using L&T PLCs, Schneider EM energy meters and an HMI. The system has four operating modes - manual solo, manual parallel, auto solo and auto parallel. In auto parallel mode, both DGs will start and synchronize to share the load when it exceeds the capacity of the individual DGs. The PLC controls starting, stopping and synchronization of the DGs based on load and maintains voltage and frequency.

1. DG-Synchronization And Load Sharing Of Two DG With
L&T-Lx-7 PLC , Schnider Conserve EM-6436 Energy meter
and Schnider HMI
 Components Used:-
o 2 Sudhir Diesel-Generator.1 0f (500KvA) and other of (320KvA).
o 1 Lx7-20ADR-6A plc along with and extension module Lx7-20EDR for
auto mode and 1Lx7-28ADR PLC (for manual mode).
o 4 Schnider conserve energy meters EM-6436.
o 1 schnider HMI (XBT-N200).
o 1 Woodward synchronization relay.
o 1 phase angle and power-factor transducer.
o 4 ACB (EDO Breaker with under-voltage relay) for Tx1 (Mains 1), Tx2
(Mains 2), DG1, and DG2.
o 1B/C ACB.(with shunt close charging motor with Under-voltage relay)
o 1 Fault relay for each DG.
 High Water Temp
 Low Lube Oil Pressure
 High Canopy Temp.
 Electrical Fault
o Solid State Buzzer for each DG.
o Amp and volt meter for each DG.
o Earth protection Fault relay for each DG.
o Reverse current relay for each DG.
o 1 Motorized POT for the master DG running in Manual Parallel and Auto
Parallel modes.
o Two reading Voltage and Frequency Meters for Parallel modes.
o 1synchroscope for Parallel mode.
o Up/Down joystick for frequency Up/Down in manual parallel and Auto
Parallel Modes.
o Under voltage relay for stabilizing the voltage below set voltage. To be
kept along with the DG output.

2.  Operating Modes:-
o 4 operating modes
 Manual solo.
 Manual Parallel
 Auto Solo.
 Auto Parallel.
o Manual solo mode:-
 In this mode the operator manually operates the on and off of DG
using start stop button.
 When both mains are absent the operator can manually operate the
dg according to the available load.
o Manual Parallel Mode:-
 This mode is useful when the total load exceeds the capacity of
first DG(DG with higher capacity),
 The operator will start the DG’s and match the Voltage and
Frequency manually.
 When the Voltage, Frequency and Phase angle are matched then
the Synchronizing relay makes the B/C ACB on.
 Thus load will be shared by both DG.
 In order to share the load as per the load capacity we have to
increase the frequency of second DG when the load on it exceeds
its capacity.
o Auto Solo Mode(Automatic Load Sharing):-
 In this Mode when the current load is less than the set max load of
the smaller DG (DG 2), DG 2 starts, DG2 ACB on and the B/C is
ON.
 When the load exceeds the DG2 max acceptable limit DG1 starts
immediately and DG2 is stop after 2min.
 When the load exceeds the max limit of DG1, DG, DG2 both are
started and B/C is OFF.
o Auto Parallel Mode:-

3.  In this Mode when the current load is less than the set max load of
the smaller DG (DG 2), DG 2 starts, DG2 ACB on and the B/C is
ON.
 When the load exceeds the DG2 max acceptable limit DG1 starts
immediately and DG2 is stop after 2min.
 When the load exceeds the max limit of DG1. Both DG’s are
started and the synch relay looks for voltage, frequency and Phase
to be matched.
 If all the three conditions are accomplished then the synch relay
makes the DG ACB ON and B/C is ON.
 Important Points:-
o While making the panel design supreme care was taken to apply all
safety measures.
o Two PLCs are used for manual and auto mode individually, so when in
any case if one of the PLC gets fail, other will be operative.
o Only one motorized pot is used, this means DG1 is master in Auto
parallel mode.
o Also the plc which is used for manual mode has additional safety
parameters which are very important.
o Both Com ports are used for communication Com 1 for communicating
the Energy meters and COM 2 for HMI.
o Also we have kept a separate Modbus enable input to PLC (R1.3) as
com2 is generally used for downloading the program. As if the com2 port
is once configured for Modbus without any enable input contact that port
will be permanently fixed for Modbus.
o L&T plc is a very cost effective plc for the DG system, and is used
instead of voltage control relay in the DG Panel.
o DG also has an electrical panel which governs the voltage and frequency
of the individual DG.
o Dg should be given start pulse of nearly 3 second but in this case
continuous start command is given and we have a separate hardwire logic
to tripping this supply.
 Important points for DG:-
o The Diesel Generator set has a, Generator, Electrical panel and AVR
(Automatic Voltage Regulator).

4. o If you don’t want to use PLC for controlling the Frequency and Voltage
then DG’s come with a special relays which synchronizes the voltage and
frequency of two DG’s being synch.
 Important points for the plc.
o The PLC being used should have a continuous supply so that it can trace
the voltage and frequency of mains and both DG’s.
o It is always preferred to give SET and RESET command for starting the
DG’s, and there ACB’s.
o There should be a delay of 5 sec for checking the live load conditions.
o Most of the program for Auto solo and Auto parallel is same only
addition is of Synchronizing mode.
 Photos:-
o Block Diagram of the system:-

5. As shown in the above figure Plc controls the start/stop, frequency inc/dec,
voltage inc/dec, controlling the ACB of mains1, mains2, Dg1, Dg2, and B/c
ACB.