PGCIL WR Network Stability STATCOMs

After the extensive blackouts in 2012 India needed to find solutions to avoid voltage collapse across the country

Background

Post the July 2012 grid collapse in India, the need for reactive power support for the transmission system was strongly recommended. Several analyses had been carried out in order to finalise the technology, size etc., which would be suitable to Indian Grid conditions. In this process, a series of meetings and discussions with various manufacturers and utilities were undertaken in order to get the best insight of the technology “state of the art” along with their opinion and feedback. To further assist with the above, Powergrid Corporation of India Ltd (PGCIL) appointed a consultant of international repute in the field of HVDC, FACTS, Power Electronics, Power Systems and T&D. After detailed deliberation, the following conclusions were arrived at:

• For dynamic compensation, STATCOM technology was proposed in view of; its better reactive power controllability, at reduced voltage it can still inject maximum current, there is no potential for creating a resonance point,  smaller installation space requirement, and higher availability due to modular design.

• The STATCOMs may be combined with mechanically switched Reactors & Capacitors controlled by STATCOM controller. The STATCOM would be primarily for dynamic compensation while the mechanically switched reactors / capacitors would be for reactive compensation under steady state.

The PGCIL Western Region (WR) was chosen as the transmission zone where the first installations of these STATCOM based dynamic reactive compensation stations.

Functional Requirement

The STATCOM Station concept for WR is a complete turnkey installation, mainly comprised of 400kV breaker, 400 kV Bus, Single phase Coupling Transformers, Medium Voltage Bus, 2 units of +150 Mvar STATCOM Units, 1 unit of 125 Mvar Mechanically Switched Capacitor (MSC), and 2 units of 125 Mvar Mechanically Switched Reactors (MSRs) connected to medium voltage bus at 38.5 kV through the necessary switchgear, control & protection system and auxiliary equipment.

 

 

Fig. 1 : Conceptual Schematic diagram of STATCOM Station

In WR STATCOM stations to the above concept are to be constructed at the Solapur, Aurangabad and Satna substations.

 

The offered STATCOM is required to achieve the following performance goals:

• Steady State Condition

The STATCOM Station (STATCOM along with MSCs and MSRs) shall provide necessary reactive power support to the 400 kV bus (PCC) to compensate for voltage variation under steady state.

• Dynamic Over-voltage Control Performance

The STATCOM shall provide necessary reactive power support with fast and smooth variation so that over-voltages under dynamic conditions are controlled. The STATCOM shall smooth out the step caused by switching of MSCs and MSRs. The operation of each STATCOM over its range of Mvar from full capacitive to full Inductive capacity and vice-versa shall be on the basis of smooth variation.

• Transient and Dynamic Stability Performances

The STATCOM Station shall provide necessary reactive power so that transient and dynamic stability of the transmission system are enhanced.

•  Damping of Power Oscillations

The STATCOM shall provide necessary damping to power oscillations by modulating its output in its entire range based on measured rate of change of power / frequency at the 400kV bus.

•  Facility for compensation of phase imbalance

With the assumption that the negative sequence voltage is 1% at rated short circuit level, the controller is required to reduce this unbalance.

•  Start up and Initial Switching:

The operation of STATCOM during start-up/ initial switching on should not create significant energizing transients causing voltage drop, voltage distortion and swinging of transmission voltage angle at the PCC bus by more than +/-5%. The compensator shall be capable of starting automatically within 10 seconds of 400 kV supply being restored following a long period with no supply at the 400 kV terminals of the compensator.

 

RXPE Solution

The RXPE team assisted PGCIL right from the planning and consulting stage. We visited the sites several times to evaluate the space requirement, existing switchgear, SCADA, etc.

When RXPE proposed their MaxiVar STATCOM they knew its design allows the STATCOM station to meet all the requirements from the client.

Wide Operating Range

The STATCOM has a wide operating voltage range. It means for a very large range of operating voltage variation, the full reactive current output of our STATCOM is available. Typically, for this reference, our STATCOM can maintain full reactive output even down to system voltages of 0.3pu.

 Multi–level Modular Solution

RXPE’s STATCOM is based on VSC multi–level inverter technology. Several inverter modules are cascaded to form one phase at the output. This allows for redundancy in modules. The redundancy permits continuous operation of STATCOM even when some modules are out of service.

Faster Response Time

The RXPE STATCOM has a faster transient and dynamic response, typically in the range of 20 milli–sec – as compared to a SVC of a similar rating. For major disturbances and blackout prevention, the fast response of reactive compensation equipment is essential.

Negligible Harmonics

The output AC voltage is created by combining multiple DC voltage levels. Excellent waveform quality is achieved without need for harmonic filters. Harmonics injected by STATCOM Station under the full operating range measured at 400 kV Bus (PCC) is in accordance with IEEE-519-1992