Mitsubishi Electric Thyristor Static Excitation Systems

Thyristor Static Excitation Systems

HEAD OFFICE: TOKYO BUILDING, 2-7-3, MARUNOUCHI, CHIYODA-KU, TOKYO 100-8310, JAPANImproper use of the products can cause severe injury or death,and may result in damage to the products and other property.
Please read the instruction manual before installing or using the products.

G-171-0-C8639-A HQ-1009 Printed in Japan (MDOC)

New publication, effective Sep. 2010
Specifications are subject to change without notice.

Thyristor Static Excitation Systems

Mitsubishi Electric’s thyristor static excitation systems are used extensively formedium- and large-capacity hydroelectric and steam-turbine generators.
They offer excellent performance, high reliability, quick response, easy maintenance and a simple structure.
Since completion of the first system in 1968, we have delivered more than 500 thyristor static excitation systems.

SystemConfigurations

The voltage regulator and potential source static excitation system functions to control the voltage of an
AC generator by directly controlling the generator's DC field current. The static excitation system iscomposed of the following;

Ratings andDimensions
The ratings of a static exciter are principally defined by the rating current and peak voltage. The typical ratings and cubicle dimensions are as follows;■Thyristor rectifier bridge and thyristor elements

Dimensions (mm)Ratings

The 3-phase, full-bridge rectifier circuit has fast response characteristics. A compact cubicle design is realized with the large on-state
current, high reversed voltage flat-pack thyristor elements, and forced air cooling. The thyristor elements are installed in a tray, andcan be exchanged during operation. For better cost performance, trayless units are also manufactured.

■Field flashing
The field flashing circuit is necessary when a generator is started, because of the selfexcitation system. A DC battery is usually used as the initial excitation power supply. An
AC power supply can also be adopted with the incorporations of rectifiers and atransformer.

■Field suppression
Immediate de-excitation is necessary when generator trouble occurs. Generally, DC
field circuit breakers are used, but a static-field circuit breaker system can be used forbetter cost-performance. These systems reduce the field energy by reversing theexcitation voltage at the rectifier gate controls, realizing rapid de-excitation.

Maximum current(A)

Maximum peakvoltage (V)

L

D

H

L1

L2

L3

L4

L5

L6

L7

1350
1100
3509
2422
8000
8000
8566
9462

460
1000
1100
1480
1100
1480
1100
1600

2900
3000
3200
3400
6000
8700
4900
6400

2000
2000
2000
2000
2500
2500
2500
2500

2300
2300
2300
2300
2600
2600
2600
2600

00000
1200
000000
1200
1200
1200
1200

900
1000
1000
1200
1200
1500
1000
1000

1000
1000
1200
1200
1200
1200
1500
1500

0000
1200
1200
0
1500

00000
1200
00

1000
1000
1000
1000
1200
1200
1200
1200

**Remarks:The ✽ mark indicates the dimensions of the trayless and static field circuit breaker system. The above dimensions are subject to change by detail and design progress.

■Over-voltage protection
C-R absorbers and varisters are installed in each AC and DC circuit to protect thethyristor elements from over-voltage. In large-capacity systems, a crowbar circuit isadapted for the DC circuit.

LL1

L2L3

L4L5L6L7■Excitation transformer
The excitation transformer reduces the supply voltage to the level required forexcitation. Generally, a dry-type transformer is used for small-capacity requirements
and an oil-type transformer for large-capacity requirements.

D=Depth■Monitoring and measurement devices
Alarm systems that warn of blown thyristor fuses, cooling-fan failure and high airtemperature are available. Additionally, a rotor temperature converter and magneticfield earth detector are optionally available.
H

Thyristor Static Excitation
System Configuration

ExcitationtransformerPT

Initialexcitation

AVRCT
41

G

Field circuit
breaker

Surge absorber

Thyristor
rectifier bridge

31

SurgeabsorberBattery
Field flashing

Surge absorber(1)

Field circuit
breakerThyristor rectifier(1)

Thyristor rectifier(2)

Thyristor rectifier(3)Surge absorber(2)