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Describtion Parallel
Operation Switching
Devices PLC
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 operating
outside of the nameplate rating:
Most
generator can be operated with a voltage-variation of 5 percent above or below
rated voltage and still safely carry rated KVA at rated power factor. However,
the manufacturer should be consulted if deviations greater than 5 percent are
anticipated. If the generator is to be operated frequency, a proportional
decrease from rated voltage and rated KVA is required. Although a reduction in
operating frequency of up to 5 percent of rated is not harmful the manufacturer
should be consulted.
Under
emergency conditions it some times becomes necessary to operate a generator in
excess of its rated KVA. Because the increased load causes increased heating of
the armature and field windings. Additional cooling must be provided to prevent
damage to the machine. In the case of selfcontained air or gas recirculation
systems, an increase in the flow of cooling water or other coolant will help
keep the temperature down.
However,
under no circumstances should the temperature of the air or gas be allowed to
reach or go below the dew point; temperatures below the dew point cause
conderrsation of any entrapped moisture on the windings of the machine.
The
accessories wanted for parallel operations.
 (1)-Paralleling
unit Aplication
This
unit is normally used for switching in parallel generating sets with either the
mains supply or with other
generating sets Sub position for switching in parallel are
1-coincidence
of the phase
2-equall
voltage
3-equall
frequancy
synchronising
unit is mmonitoring these values and gives an output impulse ,when they are
within their pre-set limits
manual
synchronization by possibly unskilled personel is dangerous and can result in
damage of the equipment it is therefore recomendable to use an automatic
synchronizing device .
frequancy
equallization can be made as follows:
1-by
manual adjustment
of the soeed
governer motor
2-automatic
frequancy
adjustment
using frequancy control unit.
after
switching in parallel start loading the generating sets:
1-
by
manual
adjustment
of the soeed governer motor
2-automatic
load
equalization
with the load balancing unit this unit gives output impulse for the speed of the
governer motor to balance the effective power to tow or more generating sets in
parallel Function
The
synchronizer unit is supplyed from one phase of each system .the unit compares
the two frequacies, the difference in voltage and measure the phase coincidence
and gives led impulse to close the alternator circuit breaker
 Permissable
switching
time
and
adjustable
of
impulse
length
Only
quick switching circuit breaker should be used ,eg. Air contactors ,magnet
operated circuit breakers choose the max permissable switching time of the
circuit breaker in thr right hand part of the diagram.
(2)
frequency
regulator :
its
main function to senses the frequency difference between the incoming machine
and the bus bar. It provide correction pulse to the electrical govemer
of the incoming diesel to speed up or slow down the generator
as required for synchronization.
With
a large frequency difference. Pulses are given in rapid succession. With little
difference pulses are given with long intervals to obtain an optimal speed
adjustment.
Average
pulse duration and interval are adjustable for adaptation to the adjusting speed
of the fuel generator. The desired nominal frequency is adjusted by means of the
spindle potentiometer. The frequency range is about 45-55 HZ or 55-65 HZ.
In
a brief the application of this unit is for controlling the frequency of the
generating unit. The unit compares the frequency of the sets or bus bar with
constant and stable frequency. And provide pulses to the motorized governors of
each set accordingly.
As
example :
Several
parallel operation gen-sets have a frequency drop dependent up on their load.
Caused by the static droop of the regulator so it provide to occur this drop.
(3)
frequency control unit :
the
frequency control unit is supplied from one phase of each system (one phase bus
bar system and one phase alternator). It operate manual or automatic.
This
unit compares the two frequencies and gives o/p impulses in the right direction
(slower or faster) to the needed governor motor the interval between the
impulses is shorter when the difference in frequency is high and longer when the
difference is low.
It's
recommended that the frequency control unit should be switch off when the
generating set is already in parallel to prevent interferences with the load
balancing unit.
(4)
voltage balancing unit :
this
unit is used for automatic voltage balancing between three-phase alternators,
preferably for paralleling alternators with the mains supply and alternators
with-out paralleled excitation systems.
The
motorized potentiometer for the voltage setting receives impulses to adjust the
required voltage.
The
unit consists of two measuring circuits, one is the main or reference supply and
the other is connected to the system which is to be balanced it is useful to
have an additional selector switch "manual-automatic".
The
unit compares the two supplied voltage and gives outgoing impulses to the
motorized potentiometer in case of high voltage difference between two systems
the intervals between the impulses are shorter and in case of lower difference
between the voltages the intervals are longer. To adept the unit to various
motorized potentiometers. The impulses are adjustable using two built-in
potentiometers.
(5)Power
relay :
The
function of power relay 'LWRI" is the automatically power adaptation for
generators. Their power o/p is record via (power) measuring transducers.
With
generators running in parallel the LWRI is
used to regulate each of them to have an identical load.
(6)Generator
power factor regulator :
The
reactive power of a mains parallel operating generator can reach undesirable
value by variations of the mains voltage. At reduced mains voltage the reactive
power o/p raises and can lead to our loading of the machine. Mains voltage
increase loads to absorption of reactive power and with that undesirable mains
load (and reactive power costs might possibly be incurred).
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