I swings (Chapter and the TCR controls may incorporate special
5 6 AN EXAMPLE OF A THYRISTOR CONTROLLER Figure 12 is a photograph of an operating air-cooled thyristor controller.
The light guides are shown near the center of the structure. The cooling air is drawn in from a plenum below the structure and the heated air is exhausted the top of the structure. The heated air leaves the room through the dampers shown at the end of the room.
Figure 13 is a photograph of a similar thyristor controller with one of
Chapter 6
.
W. LYE6.1. INTRODUCTION
This chapter provides a detailed description of a modern,
led static compensator, the Rimouski compensator installed on the ission network of Hydro at 230 The compensator is of many such installations on high-voltage transmission systems, ut many of its design features are reproduced in load compensators also, larly in supplies to electric arc furnaces. The thyristor controllers, and capacitors are essentially the same in both cases. The main erences are in the control strategy and the system voltage.
The system has many long-distance, high-voltage lines. Prior to 1978 synchronous condensers were installed o provide reactive compensation. The Baie James project, a major exten- sion of the system exploiting hydropower resources in the north of the province, will involve the transmission of more than 11,000 of power at 735 over a distance of about km, and it will have dynamic shunt compensation in the form of static compensators at five locations. Planning studies, which considered various alternative forms of compensation, led to the decision to install two static compensators for performance evaluation, at locations not on the Baie James system. One
of these was installed near Rimouski, on the system of the region. It was commissioned in 1978 and serves as a represen- tative example of a transmission system compensator.
6.2. BASIC ARRANGEMENT
compensator is a thyristor-controlled reactor with a fixed citor. Figure 1 is a simplified one-line diagram of the main
\
An Example of a Modern Static Compensator 6.3.
Description of Main Components
2 units
FIGURE 6. 31.2-MVAr bank.
between the neutral points of the two wyes to detect unbalance. h phase of each wye consists of 26 capacitor units arranged in two es groups, each having 13 units in parallel. Each unit is rated
pacitor Switches. Each wye of each capacitor bank is switched with a ree-phase, 1000-A, vacuum switch. A reactor of 30 is
h each pole to limit dildt. The switches are operated or by certain protective relays, but are never operated by the mpensator voltage regulator (as would be the case in a hybrid
ain power reactor bank consists of six air-core ure 5 and connected as in Figure 7. They are laid (Figure This arrangement is designed to coupling between the reactors. Each reactor has a s at 60 Hz and is rated 1300 A continuously;
90 A for 5 min. These are the currents required e (Figure 3). The values are rms values for the
.
The reactors also carry the harmonic d so on (see Chapter 4).ristor Controller. The thyristor controller is of the type discussed in ure and the current rating is the same as that h phase of the controller consists of four
bank in foreground. parallel for each polarity and 36 in series. The thyristors are
ted on insulating panels, together with heat sinks, resistor-capacitor
capacitor bank and gate drive circuits. A lamp monitors the
31.2 es voltage level. The thyristor panels are all
ed in a steel cubicle which forms a support structure, an air er, and a "deadfront" grounded safety barrier.
246 An of a Modern Static Compensator
\
Ohm 4 parallel
a b
FIGURE 7. Reactor bank connections
Thyristor Controller Building. This contains the three-phase thyristor controller together with its control system and protection; the station ser- vice supplies; and the thyristor cooling system (except for the evaporative cooler, which is located outdoors nearby). The building is
sheathed, thermally insulated, and can be electrically heated when neces- sary. Inside dimensions are 40 ft 37 ft 25 high.
Thyristor Switch Cooling. The thyristors are forced-air cooled. The closed-cycle air recirculates after passing through air-glycol heat ex- changers. The glycol is in turn recirculated through an evaporative cooler. Figure shows the cooling system schematically. The total air flow required is 100,000 CFM which is supplied by six fans, each rated for 20,000 CFM. One of the six fans is redundant, for reliability. Each
Air
Hear Exchanger
I
Fan
FIGURE 8. Schematic of cooling
6.3. Description of Main 247
fan has its own associated air-glycol heat exchanger and one of these also is redundant. In case the glycol system or evaporative cooling system must be shut down for any reason, an emergency system is provided whereby outside air is blown through the building by wall fans. This emergency system is satisfactory for outside air temperatures of up to about 30°C.
Compensator Protection (Figure The and buses are protected by voltage differential relays with overcurrent back-up. The ca- pacitor banks employ unbalance current detection to avoid
Zig-zag Grounding Transformer Vacuum Switch 2 4 Bus
FIGURE 9. One-line diagram showing protective relay system. Protective relay device
function numbers from ANSI Standard C37.2-1970 (as used in this figure): distance re- lay. functions when circuit impedance increases or decreases beyond limits; 49, thermai relay, functions when the temperature of a power rectifier exceeds a
mined value; ac time overcurrent relay; ac time overcurrent relay ground current: ac circuit breaker; 60, current balance relay, functions on a difference in current between two circuits; 87, protective relay, functions on a difference of two currents or some other electrical quantity.
248 An Example of a Modern Static Compensator
tor unit overvoltages due to failed capacitor elements. Fault protection is
provided by inverse relays.
Ground faults on the entire system will be detected in the neu- tral of zig-zag grounding transformer, and if not cleared by one of the primary differential systems will result in a shutdown via the ground current relays.
Fault currents associated with the power reactors and thyristor control- ler are detected by inverse overcurrent relays, and if the thyristor control- ler is unable to turn itself off and eliminate the fault, the compensator will be tripped off-line by the circuit breakers.
Overload protection for the thyristor controller includes continuous monitoring of glycol temperature and flow, air temperature and flow, and a special overload relay which monitors thyristor junction tem- perature. This relay is programmed with the thyristor
characteristics and can calculate junction temperature from a measure- ment of thyristor current.
6.4. CONTROL SYSTEM OF THYRISTOR CONTROLLER
Referring to the block diagram in Figure the control system consists basically of a voltage regulator, a current-limit, and thyristor gating
System
6.4. Control System of Thyristor Controller 249
or Voltage Operator controlled. motor
Rectifier
Current limit Transformer level adjust
I
Amplifiers
Thyristor Controlled Reactor Bank
250 An Example of a Modern Static Compensator
ther location (Auto Start). In addition all the starting functions can be performed individually by control switches in the thyristor controller building (Manual Start), The normal starting mode is Remote-Auto. The Local-Auto or Local-Manual modes are used only for maintenance procedures or in an emergency.
The automatic starting sequence has two main sections. The first starts all the auxiliary motors in an orderly timed sequence. The motors operate fans and pumps associated with the thyristor cooling system. The second section connects the compensator to the bus in a manner which causes the least disturbance to the system.
The starting sequence can be summarized as the following steps: Start auxiliary motors.
2. Close breakers.
3. Remove the gating suppression signal from the thyristors. The reactor will be energized and if the operator's setting called for the existing system voltage, the voltage regulator will call for zero current in the reactor.
4. Close the capacitor bank switches. For switching purposes the three sections of the capacitor bank are energized in sequence. As each section is energized, the voltage regulator automatically ad- justs the reactor current to maintain zero net current from the compensator.
Stopping. A complete stop, or shut-down, can be accomplished by
operator control from either Local or Remote locations, or by various protective relays. Whether the stop is initiated manually or by a protec- tive relay, the following occurs in quick sequence:
Trip circuit breakers.
2. Trip all capacitor bank vacuum switches.
3. Suppress gating of thyristors.
4. Stop cooling system motors.
6 . 5 . PERFORMANCE TESTING