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RXPE Thyristor Controlled Resistors (TCBR)

Technical Principle
Typical References
Typical Application

RXPE Thyristor Controlled Resistors (TCBR)

TCBR, short for “Thyristor Controlled Resistors” or “Thyristor Controlled Braking Resistors”, is a kind of power electronic solution to adjust/smooth the ACTIVE POWER (MW) consumption to avoid power generator trips, which is often used in “isolated power grids”.

TCBR is also used/called as Static Watt Compensator (SWC), which is very useful in isolated power grid applcations to maintain a stable power frequency and avoid power generator trips during big load impacts and/or fluctuations. 

Isolated power grids are normally weak due to lack of power generations. In this case if loads with big active power impacts can cause significant power frequency variations, which may result in generator trips. It is also known from former practice that, there are several potential risks in operating such “isolated power grid” with “impacting loads”. For example,

- If the load is suddenly lost, what will happen to the power generators?

- What will happen if the load’s power fluctuates during its operations?

- Would the power grid voltage and frequency stay stable?

With all these questions, RXPE had carried out a solution “Thyristor Controlled Braking Resistors (TCBR)” together with our SVCs that can perfectly solve such problems existing in island grids.

RXPE is capable to provide professional technical consultancy services and capable to provide customer with an overall solution to solve all these problems.

Principles

TCBR is a group of resistors that its active power can be controlled and adjusted freely and smoothly as required. It is comprised of one resistor bank (with designed MW power) and one current limiting reactor, as well as one thyristor valve to control the TCBR current, as described in Fig-1. TCBR is controlled by a control & protection system to operate at expected power (0 ~ rated MW).

Fig- 1 TCBR Principle Circuit


The connection of load and TCBR is described in Fig-2. The total power consumption = Load (Electric Arc Furnace) power + TCBR power.

The following figure shows the power of load and TCBR, we can see that when P_Load is high, P_TCBR is low, when P_Load suddenly drops, P_TCBR rises immediately, which makes the P_Total to be stable at first, if the power of load remains zero for a long time, the power of TCBR decreases slowly to around 0. The decrease speed of TCBR’s power depends on the parameters of the generator. 


Fig-2 Load and TCBR connections

Main Equipment of TCBR

1) TCBR Resistors

The resistor banks are comprised of a group of HV resistors with a certain amount of power. These resistors operate under the control of TCBR thyristor valves. The resistors will heat when operate; and such heat will be dissipated by a natural air cooling system or a forced air cooling system.


Fig- 3 Typical TCBR Resistors (Left: natural air cooling / Right: forced air cooling)

2) TCBR Thyristor Valve
Thyristor valves are composed of a number of thyristor pairs that connected in series. With different triggering pulse that feeds to each thyristor units, the valve is able to control the currents at different levels in the TCR branch. So that the TCR branch is then able to dynamically adjust its Mvar output quickly and freely.

The Thyristor valve is designed as indoor installation with carefully defined safety clearance.


Fig-4 Typical Photo of TCBR Thyristor Valves

3) TCBR Control & Protection System
The power system active power impacts are detected and monitored continuously by our advanced RXPE-11A control and protection system. The control system calculates and compensates such active power impacts by controlling the thyristor valve currents. It operate very fast, response time within 10ms.


Fig-5 RXPE-11A Control & Protection System


TCBR Compensation Performance

In order to verify the performance of TCBR, we have built a TCBR+LOAD model and simulated in PSCAD.Assuming load suddenly drop 72MW, PSCAD simulations show as follows. See Fig-6, Fig-7 and Fig-8 for more details.If no TCBR at the isolated grid, the generator frequency (in p.u. values) versus time curves is shown as follows. The horizontal axel is time, with 5 sec per division. The vertical axel is generator rotating frequency. In the following simulations, the generators are all equipped with over-speed control functions (OPC).


Fig-6 Generator Frequency at 72MW Load Rejection and No TCBR Compensation (Time: 5sec/div)

Result: Generator frequency had suddenly rised to 51.6Hz (this had exceeded the power grid frequency limits)

Fig-7 Generator Frequency Curves (Time: 5sec/div) at 72MW Load Rejection and 40MW TCBR Compensation under Auto Control

Result: Generator frequency had been limited to 50.75Hz (compensated to allowable frequency range)

Fig-8 Generator Frequency Curves (Time: 5sec/div) at 72MW Load Rejection and 70MW TCBR Compensation under Auto Control

Result: Generator frequency had been limited to 50.1Hz (the more compensation power, the better frequency performance)


RXPE is capable to provide an overall reactive power (Mvar) + active power (MW) compensation solution to those isolated power grids. Our SVC + TCBR compensation is a perfect solution to solve those voltage and frequency problems, helping customer maintain a good and stable production.

More information please contact us at overseas@rxpe.com or our 24h online service hotline +86-1834 12 12 126.
Liaoning Rongxin Xingye Power Technology Co., Ltd.