Devices and Technologies for Short Circuit Current Limitation in Power Grids

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15.07.11 The division head of the researches in the sphere of the superconductivity Victor Sytnikov (R&D Center for power engineering) made the appearance to the FGS UES management personnel
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The opening ceremony of the plant “Siemens HV devices” LLC (Voronezh) was held the 1 June 2011.

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DEVICES AND TECHNOLOGIES FOR SHORT CIRCUIT CURRENT CONTROL IN POWER GRIDS

Devices of this class are designed to limit short circuit currents and preserve stability of electric energy systems. They are particularly useful in large urban areas due to large load density that may lead to high volume of short circuit currents exceeding maximum switching capacity of existing facilities.

Several methods are available to arrest short circuit currents:

installation of current-restricting electric reactors;
electric circuit paralleling, disconnection of sectional and busbar linking switches;
step-down transformers with split low-voltage winding;
disconnecting equipment – fast-response switches with short circuit current arrest function (fuses and automatic circuit breakers);
installation of protection relays.

Background

Short circuit current limitation devices can be divided into the following two groups:

moderate capacity short circuit current limitation devices;
powerful, rapid-response short circuit current limitation devices with high voltage in short circuit modes.

The first group includes standard, low-cost and widely used shunting reactors with serial connection to the grid that allow a fairly modest degree of current arresting.

The second group’s devices are becoming more and more popular and include powerful, rapid-response units that operate on very low (ideally zero) resistance in normal operating mode but achieve required resistance values under short circuit conditions.

This group also includes high-capacity current arresters based on power electronics (Fig. 6), or on rapid-response explosive crosspoints (Fig. 7) or on high-temperature superconductors.

Power electronics-based devices consist of serially connected inductor and capacitance of equal value. Under normal operating conditions, the switch is disconnected and voltage drop is at zero. In case of short circuit, the thyristor switch closes the capacitance and the inductor (L) limits the short-circuit current.

Figure 7 shows a short-circuit current arrestor based on a magnetic inductor with a rapid-response switch in its secondary winding. In case of short circuit resistance increases automatically. A current surge and steady short-circuit current may also be limited with more depth.

They key component of a short circuit arrester is a rapid-response switch element made of three main elements:

a rapid-response disconnecting device;
a parallel fuse
a logic circuit block with current transformer.

Under normal operating conditions the current flows through a copper busbar installed in the holder of a disconnecting switch. The fuse current is approximately 0.1% of that current’s value.

In the event of short circuit, when the current force exceeds a predetermined ceiling, logic circuits generate a signal to trigger a pyrotechnic busbar blowout, following which the current is fully rerouted to a switch, thus removing the possibility of switching surges. Triggered by protection relay automatics signal, logic circuit initiate a command for contact closing at the rapid-response closer, following which the device returns to its original status.

A typical switch element consists of a regularly closed (1) and regularly open (2) contacts. The exact number of elements depends on specific operating conditions. Currently multiple research projects on superconductor current arresters are underway in Russia and abroad; samples and prototypes have been created, and according to several expert assessments, commercial application may begin around 2015.

Parameter	Superconductor SC current arrestor	Semiconductor SC current arrestor	Short circuit current arrestor switch
U, nominal	3,6-154	110 kV	6-220
I, nominal kA	Up to 4	4	10
Activation time (sec)^*	0,001-0,002	0,005	0,001-0,002
Restoration time (sec)	1-2	0,001	0,001-0,002
Functional concept	Resistance increase	Resistance activation	Resistance increase
Activation under short circuit conditions	Material qualities	Operation system	Operation system
Status	Samples and prototypes under production	Manufactured by Siemens Co.	A prototype rated for 20 kV has been built and tested. Not made commercially so far.

* covers only the operation time of the device itself

DC links are also capable of serving as current arresters; however, they have many other applications and using them only for current arresting purposes is not cost efficient.