Hello learners, welcome to this topic on compact substation. At the end of this topic, you will be able to: describe compact substation, identify the components of compact substation, list the key specification and tests of compact substation. Compact substation, CSS, is an assembly comprising an enclosure containing medium voltage MV switch gear, distribution transformers, low voltage LV switchboards, connections, and auxiliary equipment to supply a low voltage energy from medium voltage systems. CSS forms part of MV distribution ring network. With the advantage of compact size, prefabricated compact substation was widely used in the three phases of the power distribution system, 11 KV-33 KV. The following images show the 3D model of a compact substation. The substation is basically designed in the form of a container as shown. Let's see how it looks from inside. The image shown here shows the substation without the top. The space is hollow before placing any equipment. At one of the narrow ends, there is an entry for the personnel and other equipment movement. Now you can see that some electrical panels are placed inside the substation. Each panel is given a tag or a number for identification. For example, the panel number 9 is the LV switchboard. Similarly, as shown, we have some of the electrical panels. Now we see how the CSS is placed on a foundation and there's way walk to enter the substation. This is another view from the bottom side after the substitution is placed on the foundation. Finally, here is the view after the substitution is erected on the foundation. The main components of a prefabricated package substation are: transformer, high voltage switch gear control gear, low voltage switch gear control gear, and corresponding interconnections, that is cable, flexible bus bars, and auxiliary equipment, and 11 KV RMU. The components shall be enclosed by either common enclosure or by an assembly of enclosure. Common configuration of RMU is, three-way with two load Break switches plus one vacuum circuit breaker. The following are the key specification of compact substation. Rated voltage, MV or LV, rated current, MV or LV, rated power frequency withstand voltage, rated lightning impulse withstand voltage, rated short-time current rating, MV or LV, dimensions, IP class, MV or transformer, or LV, temperature class. The image is a typical single line diagram of a compact substation. The type tests for CSS-HV switch gear are as follows: impulse test with breaker inside the cubicle, temperature rise test with breaker inside the cubicle, short-circuit tests with breaker inside the breaker, dielectric tests, test of apparatus, that is, circuit breaker and earthing switch, arc fault test, internal arc test for 21kA for one second. The following are the acceptance tests for CSS-HV switchgear : withstand voltage at power frequency for all current carrying parts, including wiring, measurement of resistance of the main circuit, gas leakage test, withstand voltage on auxiliary circuits, operation of functional locks, interlocks, signaling devices, and auxiliary devices, suitability and correct operation of protections, control instruments and electrical connections of the circuit breaker operating mechanism, primary and secondary injection, verification of wiring, visual inspection. The type tests for CSS-HV switch gear are as follows: measurement of winding resistance, measurement of voltage ratio and check the voltage vector relationship, measurement of impedance voltage, that is, principal tapping, short circuit impedance and load loss all shall be corrected to a temperature of 75 degrees Celsius, measurement of no load loss and current, separate sources withstand voltage, induced over voltage withstand, dielectric test of oil. The following are the acceptance tests for CSS-HV switchgear: type test, short-circuit test, acoustic noise level test, oil leakage test by application of pressure. In this session, we have described compact substation, identified the components of compact substation, listed the key specifications and tests of compact substation.
