LSC Loss of Service Continuity Categories (IEC 62271-200)

Short answer

When a high-voltage compartment of a switchgear panel is opened for inspection or maintenance, the question is what remains energized. IEC 62271-200, 2011 edition, answers with the loss of service continuity category, LSC. It is a characteristic of each functional unit, and the standard defines it in clause 3.131. There are four categories: LSC1, LSC2, LSC2A and LSC2B.

The four categories

The LSC2 family (LSC2, LSC2A and LSC2B) seeks maximum network continuity during access. To achieve it, at least one busbar is kept energized. A movable inserted partition can be used to reach the category.

What “accessible” means

The standard distinguishes high-voltage compartments by how they are opened. The accessible ones are classified as follows:

• Interlock-controlled. Interlocks ensure that all live parts are de-energized and earthed before opening, or are in the disconnected position with the shutters closed.
• Procedure-based. Safety depends on the user’s procedure and on locking. The compartment has provision for padlocks or equivalent.
• Tool-based. No built-in feature ensures safety before opening. Tools are needed to open them.

The first two types are intended for normal operation and maintenance, and their covers or doors do not require tools. The third normally indicates that the user must take other measures to ensure safety. Compartments that cannot be opened, such as a welded tank of a panel with insulating gas, are called non-accessible.

Examples from the standard

The standard illustrates the categories with figures 101 to 106:

1. LSC1 (figure 101). A unit whose cable connections are in the same compartment as the circuit breaker and the busbar.
2. LSC2 (figure 102). A unit with a fixed circuit breaker and two accessible compartments other than the busbar, with a disconnector in the circuit breaker compartment. Opening the circuit breaker compartment with the busbar energized is not allowed. If there is a complete partition between the connection compartment and the circuit breaker compartment, the connection compartment can be opened with the busbar energized.
3. LSC2 (figure 103). A unit with circuit breaker and cables in the same compartment, accessible with the busbar energized because a disconnector and an earthing switch, located in the busbar compartment, isolate it and earth it. A typical ring main unit (RMU), with the busbar compartment containing the switch-disconnectors of several units, is also designated LSC2.
4. LSC2A (figure 104). Like the second example, but with the disconnector in the busbar compartment and a complete partition between the busbar and the circuit breaker. The circuit breaker compartment and the connection compartment can be opened with the busbar energized, once the disconnector is open and the earthing switch closed. To access the circuit breaker compartment, the cables must be de-energized and earthed.
5. LSC2B (figure 105), non-withdrawable design. Like the previous example, but with a second disconnector and an earthing switch in the connection compartment, with a complete partition. It allows opening the circuit breaker compartment with the busbar and the connection compartment energized.
6. LSC2B (figure 106), withdrawable design. If the circuit breaker of each unit has its own accessible compartment, it can be serviced without de-energizing the connection compartment. That requires, as a minimum, three compartments per unit: one for the circuit breaker, one for the components on one side (for example, the feeder) and one for those on the other side (for example, the busbar). In a double busbar, each busbar goes in a separate compartment.

Which category to specify

The standard warns that how far it is worth opening compartments with the installation energized depends on several aspects of the installation, and that the category does not measure the quality of the switchgear. To choose, it helps to ask:

• Which part of the installation cannot be left without supply during maintenance?
• Is there an alternative supply on the cable side (ring operation, generators)? For those cases LSC2B can be specified, which keeps the connection energized.
• Is it acceptable to take the whole busbar section out of service? If so, LSC1 may be enough.

The LSC category goes in the list of data supplied with the enquiry or the order (clause 9.1), together with the partition class (PM or PI).

The partitions and shutters that support the category are described in partition classes PM and PI. The category is combined with the internal arc classification (IAC) when choosing the switchgear. The assembly is presented in medium-voltage switchgear, and interlocks in withdrawable truck and interlocks.

What not to do

• Do not confuse LSC with IAC. LSC deals with service continuity; IAC deals with protecting people against an internal arc.
• Do not assume LSC2A because the panel has shutters: the category depends on the design of compartments, disconnectors and partitions.
• Do not open an accessible compartment with the busbar energized if the panel is not classified for it.
• Do not treat the LSC of one panel as that of the whole section: the category is assigned to each functional unit.

When to call us

At Tiza Group we review with you the interlocks, the positions and the tests of your medium-voltage switchgear before it goes into service. Learn about our medium-voltage switchgear testing service. Write to us and we will quote it. Field testing is done in Colombia, or elsewhere on request.

Related guides

• Partition classes PM and PI in medium-voltage switchgear
• Internal arc classification IAC of a switchgear panel
• Medium-voltage switchgear: parts, functions and tests
• Withdrawable truck of switchgear: positions and interlocks
• Interlocks in medium-voltage switchgear and RMUs

References

• IEC 62271-200, High-voltage switchgear and controlgear - Part 200: AC metal-enclosed switchgear and controlgear for rated voltages above 1 kV and up to and including 52 kV, 2011 edition, clauses 3.131 (3.131.1 to 3.131.2), 8.103.2, 8.103.3 and 9.1, and figures 101 to 106.

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