A.V.R

AUTOMATIC VOLTAGE REGULATOR

DIFINITIONS:-

1. Voltage regulation:In a power supply, the automatic holding of the output voltage to a constant value, despite variations in the input voltage or load resistance.

2. Current regulation:In a power supply, the automatic holding of the output current to a constant value, despite variations in the input voltage or load resistance.

3. Automatic voltage regulator (AVR) :An automatic feedback control system that is responsible for maintaining a scheduled voltage either at the terminals of a synchronous generator or at the high-side bus of the generator stepup transformer. The control is brought about by changing the level of excitation.

A.V.R.

C.T. FEED BACK

V.T. FEED BACK

INPUT (power supply)

FIELD

C.T. FOR CURRENT FEED BACK SIGNAL TO AVR

GENERATOR

V.T. FOR VOLTAGE FEED BACK SIGNAL TO AVR

EXCITER

A.V.R.

A.V.R. DC O/P TO EXCITER

PERMANT MAGNET ( AVR POWER SUPPLY)

PERMANT MAGNET THERMAL PROTECTION

SIMPLE GENERAL CIRCUIT

A.V.R. I/P(POWER SUPPLY)

PERMANT MAGNET FLASHING

• AVR (I/P or POWER SUPPLY) is the method that enables the machine to build up its voltage.

HOW CAN WE TEST AVR?

To test AVR we should provide the three indicated i/p elements :

1. Feed back signal from the generator o/p current.2. Feed back signal from the generator o/p voltage.3. A method to supply AVR itself.

•The test we made ,was on the AVR of the emergency generator & its power supply is a permanent magnet type.

380/200v(voltage signal from Gen. o/p) M5

Main boardM3

Trip/Reset

M2 O.C. protection

M1Sensing & control

M4Excitation o/p card

Filteringcapacitor

Terminal strip

To supply AVRBy 110v ac from

Permanent magnet

Rectificationbridges

M4 CardExcitation o/p card

Variable resistor For tuning voltage

Variable resistor For tuning droop

Variable resistor For tuning gain

Ac power supplyI/P

From permanent magnet

R S T380v ac

Gen. o/p voltage signal

o/p dc voltage To Exciter

For simulation testing circuit ,we used:

1. 110v ac power supply that represents the permanent magnet supply.2. 380v ac (R-S-T) that represents the voltage gen. o/p signal to test the main board.3. Lamp at the o/p terminals.

The lamp position

Light (The circuit is ok)

Dark(There is a problem in the circuit)

So check terminations ,transformers , all cards ,capacitor ,rectification circuit

& so on

• We have a reference values which were taken from the actual operation from another tuned AVR works in the current time on the machine:1. Be sure that the two V.T. ‘s which feed by the Gen. o/p voltage to feed back the AVRBy the voltage signal have the correct turns ratio (380/200v – for the new AVR’s) or (380/380v – for the old AVR’s).2. If we applied the 73v ac on the AVR i/p terminals (points 11,12&13 in terminal strip)We get 97v dc on the AVR o/p terminals (points F1&F2 in terminal strip).

• When making this test we cared about testing the all circuit of AVR so ,we only powerSupplied the AVR by 73v ac on its i/p & noted the o/p (lamp position). If the lamp is dark We started to make our checks :1. At first we apply 380v ac (represents the voltage gen. o/p signal )to test the the V.T.s& the main board. If it’s ok ,we go to the second step…2. Check the filtering capacitor. If ok…3. Check the rectification bridges by checking its diodes individually (by measuring each diode between anode & cathode (0.7 v) between cathode & anode (open). Also by checkingthe bridges loop completely). If ok…4. By try & error check all cards M1,M2,M3,M4 & M5.

• After finishing laboratory checks ,we must make an actual check on the machine to testIf we get the wanted o/p voltage from the machine or not ,check the machine response && also to check the machine stability at Running conditions under no load & load operation.

Cards tuning resistors values for stable operation

M1 CardSensing & control card

Variable resistance to tune the card

For voltage (0.82 kΩ)

For droop (98.2 Ω)

For gain(0.82 .779 kΩ)

M2 CardOver current protection card

Variable resistance to tune the card

(0.667 kΩ)

My Regards

Eng. Mohamed Saied