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3. System power-up (Standard Version)
Before the system is powered-up for the first time the following checks should be carried
out by qualified personnel only.
A)
Inspect the input and output terminations for tightness, correct wiring and phase rotation.
B)
Check that the building electrical service is of sufficient capacity to supply the input current of the AVR,
remembering that this can be 40% higher than the output current to the load.
C)
Check building electrical service is of correct nominal voltage and wiring configuration and that main
circuit breakers are suitable for the inductive nature of the load represented by the AVR.
D)
Ensure that the load equipment is ready to be energised. Once the above conditions have been verified,
input power may be applied to the AVR. Once input power is applied the three digital voltage meters on the door
of the AVR should indicate a valid output voltage. If this is not the case switch off the power immediately and
refer to the troubleshooting section of this manual. The AVS indicators on the door (if fitted) should show 'on'
(after the wait time of 3 minutes).
3. System power-up (DS Version)
Before the system is powered-up for the first time the following checks should be carried out by qualified
personnel only.
A)
Inspect the input and output terminations for tightness, correct wiring and phase rotation.
B)
Check that the building electrical service is of sufficient capacity to supply the input current of the AVR,
remembering that this can be 40% higher than the output current to the load.
C)
Check building electrical service is of correct nominal voltage and wiring configuration and that main
circuit breakers are suitable for the inductive nature of the load represented by the AVR.
D)
Ensure that the load equipment is ready to be energised. Once the above conditions have been verified,
input power may be applied to the AVR. It is wise to apply power to the AVR with the input breaker in the 'on'
position and the output breaker in the 'off ' position.
Once input power is applied the three digital voltage meters on the door of the AVR should indicate a valid
output voltage. If this is not the case switch off the power immediately and refer to the troubleshooting section
of this manual. The AVS indicators on the door should show 'on' (after the wait time of 3 minutes). When it has
been verified above that the AVR is functioning correctly, the incoming power should be switched off and the
output circuit breaker set to the on position. If power is now re-applied, the load will be automatically supplied
when the 3 minute delay time has elapsed.
4. Functional Description
4.1 General Function
This three phase AVR is made up from three identical single phase regulator units. Each of these monitors its own
output voltage and adjusts for variations in mains supply voltage so as to maintain an output voltage within close
limits. When the AVS function is fitted the outputs from the regulators are connected through a
contactor to the load. The contactor is controlled by a three phase Automatic Voltage Switcher PCB which
monitors the AVR outputs. This connects the load only when all the phase voltages are within acceptable limits.
There is a delay between the time when all voltages come within limits and the contactor switching on. This is so
as to allow the supply to stabilise and to avoid repeated switching of the load on and off should the mains supply
be exceptionally erratic. The state of the AVS circuit is indicated on the front panel by three large LEDs, Green for
On, Yellow for Wait and Red for Off.
4.2 AVR Function
This is based on an auto transformer with tap changing on the output. There are seven taps to each transformer
giving an accurate output voltage for a wide range of input voltage. The taps are switched by generously rated
THREE PHASE AUTOMATIC VOLTAGE REGULATOR Issue: Feb 2002
THREE PHASE AUTOMATIC VOLTAGE REGULATOR Issue: Feb 2002
Triac banks to cope with motor start loads. Low value resistors are fitted with each Triac to ensure that high
currents are shared equally between the Triacs within each bank. This technique results in a voltage stabiliser
which has no moving parts, responds quickly to voltage fluctuations and is not as large or heavy as other AVRs
utilising different regulation techniques.
A micro-controller forms the heart of the control system. It measures the AVR output voltage and turns on the
appropriate Triac bank to select the correct tap. A potentiometer is provided for fine adjustment of the output
voltage. The micro-controller also measures the frequency of the mains supply and compensates accordingly. This
also means that the AVR will work over a frequency range of 45 - 88Hz automatically and down to as low as 30Hz
for short periods to help cope with diesel generator loading problems.
Frequency and voltage measurements are filtered by the circuit and software to remove noise and so prevent
spurious tap changes.
A watchdog function is implemented in the micro controller. This independently monitors the operation of the
micro-controller and its software. If it detects a malfunction, it will reset the micro and re-initialise the control
system.
The low voltage DC supply to the control circuit is also protected by a fuse.
Additionally, a hardware reset circuit is included which monitors the supply rail for the control circuit. If the
mains is so low that the control circuit will not function correctly, the monitor circuit will put the micro-
controller into the reset state and turn off all Triacs.
When the mains supply increases to a usable level, the monitor circuit will restart the micro and the system will
re-initialise. This ensures an orderly and controlled restart from a brownout or blackout condition. The circuit
is designed with a large hysteresis so that the unit will not attempt to turn on again until the supply voltage is
sufficient to withstand possible starting surges. This avoids the possibility of such a surge of current causing the
supply to dip sufficiently to turn the unit off again.
Additional protection is provided by temperature sensors fitted to each transformer. If the AVR is used at full
load and either the ambient temperature is excessively high or the ventilation grills have been obstructed, the
temperature of the transformer may increase beyond reasonable limits. In such an event, the temperature sensor
will disconnect the supply to the corresponding control board and thereby turn the output off. When the
transformer has cooled sufficiently, the sensor will restart the AVR.
When restarting after the above condition the AVR may cause equipment to begin to operate suddenly. Steps
should be taken to ensure that this does not expose persons to risk.
4.3 AVS Function [Optional - has to be ordered separately at time of purchase]
4.3.1 General Description
The Automatic Voltage Switcher (AVS) is a device for the protection of electrical equipment against fluctuations,
interruptions and other abnormalities in the electricity mains supply.
The Three Phase AVS monitors various parameters of the mains supply, and keeps it connected to the equipment
so long as all the parameters are within defined acceptable limits. This is the normal condition and it is indicated
by a Green LED (light emitting diode). If the mains voltage goes outside these limits, the AVS disconnects the
equipment from the mains and this is indicated by the Red LED (In some options, it is possible to
select indication only without disconnection's.) When the mains supply returns within the acceptable limits,
indicated by an Amber LED, the mains remain disconnect from the equipment during the wait time, set to a
nominal 1 minute by factory selected components. If during the wait time the mains again goes outside the
limits, the wait time starts from the beginning. At the end of the wait time, when the mains supply has been
continuously within the limits for its duration, normal condition returns indicated by the Green LED, and the
equipment is re-connected to the mains.
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