Automatic Power Factor Controllers
Various types of automatic power factor controls are available with relay / microprocessor
logic. Two of the most common controls are: Voltage Control and kVAr Control
logic. Two of the most common controls are: Voltage Control and kVAr Control
Voltage Control
Voltage alone can be used as a source of intelligence when the switched capacitors are
applied at point where the circuit voltage decreases as circuit load increases. Generally, where
they are applied the voltage should decrease as circuit load increases and the drop in voltage
should be around 4 – 5 % with increasing load.
Voltage is the most common type of intelligence used in substation applications, when
maintaining a particular voltage is of prime importance. This type of control is independent of
load cycle. During light load time and low source voltage, this may give leading PF at the substation,
which is to be taken note of.
applied at point where the circuit voltage decreases as circuit load increases. Generally, where
they are applied the voltage should decrease as circuit load increases and the drop in voltage
should be around 4 – 5 % with increasing load.
Voltage is the most common type of intelligence used in substation applications, when
maintaining a particular voltage is of prime importance. This type of control is independent of
load cycle. During light load time and low source voltage, this may give leading PF at the substation,
which is to be taken note of.
KVAR Control
Kilovar sensitive controls are used at locationswhere the voltage level isclosely regulated and not available as a control variable. The capacitors can be switched to respond to a decreasing power factor as a result of change in system loading. This type of control can also be used to avoid penalty on low power factor by adding capacitors in steps as the system power factor begins to lag behind the desired value. Kilovar control requires two inputs - current and voltage from the incoming feeder, which are fed to the PF correction mechanism, either the microprocessor or the relay.
Automatic Power Factor Control Relay
It controls the power factor of the installation by giving signals to switch on or off power factor
correction capacitors. Relay is the brain of control circuit and needs contactors of appropriate
rating for switching on/off the capacitors.
There is a built-in power factor transducer, which measures the power factor of
the installation and converts it to a DC voltage of appropriate polarity. This is compared with
a reference voltage, which can be set by means of a knob calibrated in terms of power factor.
correction capacitors. Relay is the brain of control circuit and needs contactors of appropriate
rating for switching on/off the capacitors.
There is a built-in power factor transducer, which measures the power factor of
the installation and converts it to a DC voltage of appropriate polarity. This is compared with
a reference voltage, which can be set by means of a knob calibrated in terms of power factor.
When the power factor falls below setting, the capacitors are switched on in sequence. The
relays are provided with First in First out (FIFO) and First in Last Out (FILO) sequence. The
capacitors controlled by the relay must be of the same rating and they are switched on/off in linear
sequence. To prevent over correction hunting, a dead band is provided. This setting determines
the range of phase angle over which the relay does not respond; only when the PF goes
beyond this range, the relay acts. When the load is low, the effect of the capacitors is more pronounced
and may lead to hunting. Under current blocking (low current cut out) shuts off the
relay, switching off all capacitors one by one in sequence, when load current is below setting.
Special timing sequences ensure that capacitors are fully discharged before they are switched
in. This avoids dangerous over voltage transient. The solid state indicating lamps (LEDS) display
various functions that the operator should know and also and indicate each capacitor
switching stage.
relays are provided with First in First out (FIFO) and First in Last Out (FILO) sequence. The
capacitors controlled by the relay must be of the same rating and they are switched on/off in linear
sequence. To prevent over correction hunting, a dead band is provided. This setting determines
the range of phase angle over which the relay does not respond; only when the PF goes
beyond this range, the relay acts. When the load is low, the effect of the capacitors is more pronounced
and may lead to hunting. Under current blocking (low current cut out) shuts off the
relay, switching off all capacitors one by one in sequence, when load current is below setting.
Special timing sequences ensure that capacitors are fully discharged before they are switched
in. This avoids dangerous over voltage transient. The solid state indicating lamps (LEDS) display
various functions that the operator should know and also and indicate each capacitor
switching stage.
Intelligent Power Factor Controller (IPFC)
This controller determines the rating of capacitance connected in each step during the first hour
of its operation and stores them in memory. Based on this measurement, the IPFC switches on
the most appropriate steps, thus eliminating the hunting problems normally associated with
capacitor switching.
of its operation and stores them in memory. Based on this measurement, the IPFC switches on
the most appropriate steps, thus eliminating the hunting problems normally associated with
capacitor switching.