PI Manufacturing AC generators - Manual (Page 19)

SECTION 6
ACCESSORIES
Generator control accessories may be fitted, as an option, in
the generator terminal box. If fitted at the time of supply, the
wiring diagram(s) in the back of this book shows the
connections. When the options are supplied separately, fitting
instructions are provided with the accessory.
The following matrix indicates availability of accessories with
the differing AVRs.
Note the SX460 is not suitable for operation with accessories.
AVR Model
Paralleling
Droop or
Astatic
Manual
Voltage
Regulator
Var/PF
Control
Current
Limit
SX460 X X X X
AS440 O O O
MX341 O O O
MX321 O O O
6.1 REMOTE VOLTAGE ADJUST (ALL AVR TYPES)
A remote voltage adjust (hand trimmer) can be fitted.
SX460
Remove link 1-2 on the AVR and
connect adjuster to terminals 1 and 2.
AS440
Remove link 1-2 at the auxiliary
terminals
MX341 and MX321 and connect adjuster to terminals 1
and 2.
6.2 PARALLEL OPERATION
Understanding of the following notes on parallel operation is
useful before attempting the fitting or setting of the droop kit
accessory. When operating in parallel with other generators or
the mains, it is essential that the phase sequence of the
incoming generator matches that of the busbar and also that
all of the following conditions are met before the circuit
breaker of the incoming generator is closed on to the busbar
(or operational generator).
1. Frequency must match within close limits.
2. Voltages must match within close limits.
3. Phase angle of voltages must match within close limits.
A variety of techniques, varying from simple
synchronising lamps to fully automatic synchronisers, can
be used to ensure these conditions are met.
Important ! Failure to meet conditions 1, 2, and 3 when
closing the cricuit breaker, will generate
excessive mechanical and electrical
stresses, resulting in equipment damage.
Once connected in parallel a minimum instrumentation level
per generator of voltmeter, ammeter, wattmeter (measuring
total power per generator), and frequency meter is required in
order to adjust the engine and generator controls to share kW
in relation to engine ratings and kVAr in relation to generator
ratings.
It is important to recognise that :
1. True kW are derived from the engine, and speed
governor characteristics determine the kW sharing
between sets
and
2. kVAr are derived from the generator, and excitation
control characteristics determine the kVAr sharing.
Reference should be made to the generating set
manufacturer's instructions for setting the governor
controls.
6.2.1 DROOP
The most commonly used method of kVAr sharing is to create
a generator voltage characteristic which falls with decreasing
power factor (increasing kVAr). This is achieved with a current
transformer (C.T.) which provides a signal dependent on
current phase angle (i.e. power factor) to the AVR.
The current transformer has a burden resistor on the AVR
board, and a percentage of the burden resistor voltage is
summed into the AVR circuit. Increasing droop is obtained by
turning the DROOP control potentiometer clockwise.
The diagrams below indicate the effect of droop in a simple
two generator system
: -