New Electric Machine Compensators of Reactive Power

8/11/2019 New Electric Machine Compensators of Reactive Power

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New Electric Machine Compensators of Reactive Powerwith Double-Axis Excitation

Y. G. SHAKARYAN,

P. V. SOKUR*,

T. V. PLOTNIKOVA,

I. Y. DOVGANJUK,

R. D. MNEV

Research & Development Center for

Power Engineering

(Russia)

N. D. PINCHUK,

O. V. ANTONUK,

M. B. ROYTGARTZ,

D. V. ZHUKOV

Power Machines

(Russia)

Y. A. DEMENTYEV

V. M. SEDUNOV

Federal Grid Company of

United Energy System

(Russia)

SUMMARY

As a result of collaboration of R&D CENTER FOR POWER ENGINEERING and plant

Electrosila a new type of the electromachine compensators of reactive power by the capacity

100 MVA with the two-axial excitation and vector control has been designed, constructed and

put into operation. The paper describes the benefits of the compensator, its technical and designcharacteristics, as well as a way to control reactive power and electromagnetic torque and shows

the results of experience in reverse reactive power.

The possibility of production of flywheel-compensator, working with variable speed to

compensate fluctuations of active network power and technical advantages of this modification

was considered.

KEYWORDS

Asynchronous machine - doubly-fed machine - reactive power compensator - voltage control-

variable speed - flywheel storage.

*[email protected]

21, rue dArtois, F-75008 PARIS CIGRE 2012http : //www.cigre.org A1-101


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A reactive power compensator is one of the important components of modern power grids,

designed to maintain voltage in grid nodes and reduce active power losses through choosing the

optimum conditions.

Over the recent time, power systems have widely used static compensators based on power

electronics. Alongside with clear advantages (fast speed of operation, no rotating parts), they

have drawbacks as well (harmonics generation, dependence of reactive power on connection

point voltage).As distinct from static devices, however, electric machine compensators can withstand short-

time double overloads, which in the case of static devices may only be reached by doubling the

installed capacity. Another important property is resistance to potential surge overvoltages in

lines (caused, for example, by thunderstorm activity).

Research & Development Center for Power Engineering in cooperation with Power Machines

developed, manufactured and placed into operation a new ASK-100-4 electric machine

compensator of reactive power with double-axis excitation and capacity of 100 MV. The

ASK-100-4 compensator is designed for operation in steady state conditions at synchronous

speed. Development and manufacture allowed for the experience of designing double-axis

excitation turbogenerators [1].

The two excitation windings with excitation system and vector control provide new propertiesand advantages to such compensators as compared to traditional synchronous compensators with

one excitation winding:

1. Extended reactive power range from +100 MVAr to -100 MVAr (traditional synchronous

compensators have the range from +100 MVAr to -40 MVAr).

2. Faster reactive power (voltage) control speed due to current reversing in excitation

windings.

3. Improved damping of oscillation in response to grid disturbances.

4. Enhanced survivability due to the possibility of operation in backup modes in case of

excitation system failures.

Two ASK-100-4 compensators are installed at Beskudnikovo substation in Moscow. Their basic

specifications are listed in Table 1 and outline drawing is shown in Fig. 1.

Table 1

Parameter Value

Rated power, MV 100

Reactive power,VAr 100

Stator voltage, kV 20

Stator current, 2,900

Rotor winding current:

on axis d,

on axis q,

2,200

740

Speed, rpm 1,500Total loss in compensator, kW 1,500

The compensator is air-cooled throughout, including oil and bearings. Losses generated in stator

and rotor windings as well as in magnetic cores (in the stator core and the stator shaft) are

withdrawn by direct air-cooling of the stator core and indirect air-cooling of stator and rotor

windings.

The compensator has an open-circuit cooling system with outside air taken in through an air

treatment unit and heated air added in cold weather.

The stator winding face parts are of basket type. Winding bars braided from solid conductor

strands have transpositions in slotted and face parts. The bars are sealed in the slots by gaskets of

semiconducting material and secured with special fiberglass wedges and corrugated woven-glassreinforced liners. The bars have Class F continuous thermoreactive insulation.


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Leakage fluxes of the stator winding face parts are damped by copper screens and electric steel

shunts installed under locking rings.

Fig. 1. Outline Drawing of ASK-100-4 Compensator

The rotor is made from a solid forging of special steel providing its mechanical strength in allselected operating modes of the compensator.

The primary and control excitation windings are placed in the slots. Both slot and turn insulation

of coils is made of fiberglass impregnated with heat-resistance epoxy lacquers (Class F). The

winding is indirectly cooled by air circulating in subslot and radial channels and in the rotor

body tooth splines.

Influence of negative-sequence currents in unbalanced conditions is diminished by the rotor

damping system composed of wedges, flat copper gaskets located beneath wedges and short-

circuit copper segments in the banding space.

Mounted from two sides of the compensator are brush rigs designed to supply excitation current

to slip rings of the rotors primary and control windings. The compensator has static thyristor

reverse excitation.A thyristor starting device is used for standstill-rotor start and shutdown of the compensator

(including those in emergency conditions with minimized shutdown time).

The compensator features a measuring and diagnostic system that monitors relevant values,

records and warns about any departures from the preset limits.

It is evident from the vector diagram (Fig.2) showing the operation of the double-axis excitation

compensator in various conditions that the excitation current if is comprised of two

components: primary excitation winding current ifd and control excitation winding current

ifq. The control excitation winding contains fewer turns and lower rated current than the

primary excitation winding. MMF of the former is 6% of MMF of the latter.

The control excitation winding is responsible for electromagnetic torque control, thereby

providing static stability in the in-depth reactive power consumption mode.

Air supply from air filter unit

Air release to air filter unit


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As seen from the vector diagram, the in-depth reactive power consumption mode (Q) is provided

by current reversing in the primary excitation winding. This enables high speed of reactive

power control.

Q=0

Fig. 2. Vector Diagram of ASK-100-4 Operation in Reactive Power Output and Consumption

Conditions

Figure 3 depicts a transient process at the reverse flow of ASK-100-4 reactive power. The

experiment involved a stepwise change of the automatic voltage regulator (AVR) setting from

the initial value U=1.14 p.u. to U=0.84 p.u. for the time t=7 sec, followed by the restoration of

the initial setting value. With selected voltage setting values, the compensator operates first in

the reactive power output mode (Q=1.14 p.u.) and then changes over to the in-depth reactive

power consumption mode (Q=-0.84 p.u.) at the rated stator current i=1 p.u.

The compensators reactive power reverse flow is caused by ifd current reversing in the

primary excitation winding. The angular position of the ASK rotor (Delta) during the reactive

power reverse flow remains almost unchanged. The reactive power reverse process is

dynamically stable. A new value of voltage across the generator busbars sets after about 0.8 secand does not differ by more than 5% from the setting. The maximum change rate of the

compensator reactive power is 300dt

dQMVAr/sec.


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Fig. 3. ASK-100-4 Compensator Reactive Power Reverse Flow

1 stator voltage; 2 reactive power; 3 stator current; 4 d winding excitation current; 5 qwinding excitation current; 6 rotor angular position.

With various failures in the excitation system, the compensator can operate in backup modes:

with primary winding excitation only (-30 MVAr


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vector type excitation system for wide-range reactive power control. CIGRE, 2010

Session, paper A1-108, p. 8.

Documents

New Electric Machine Compensators of Reactive Power