Disconnector Position: Locking and Indication

Short answer

A disconnector is operated with no appreciable current and, when open, provides the isolating distance between two parts of the installation. Its position therefore cannot be an assumption. IEC 62271-102 (2001 edition with Amendment 1:2011 and Amendment 2:2013) gathers three requirements in clause 5.104:

Securing the position: clause 5.104.1

Disconnectors and earthing switches, with their mechanisms, must be designed so that they cannot leave their open or closed position through:

• Gravity.
• Wind pressure.
• Vibration.
• Reasonable shocks.
• Accidental contact with the operating-system rods.

They must also allow temporary mechanical locking, both open and closed, for safety, for example during maintenance. This last requirement does not apply to hot-stick operated equipment.

For motor-operated mechanisms, clause 5.104.2 also requires a means of manual operation. When the manual device, for example a crank, is engaged, the motor’s control energy must be safely interrupted.

Indicating the position: clause 5.104.3.1

It must be possible to know the position of the disconnector. For the open position, the standard considers this met in either of two cases:

• The isolating distance or gap is visible.
• The position of each moving contact that ensures that distance is shown by a reliable visual device.

The standard notes that, in some countries, the disconnector design is such that the isolating distance is visible.

The indicator is considered reliable when its kinematic chain, from the moving contacts to the indicator, meets these conditions:

• It is a continuous mechanical connection, so that the drive is positive.
• It has enough mechanical strength to pass the tests of Annex A.
• The force-limiting device, if any, is not part of that chain.

The indicator may be marked directly on a mechanical part of the power chain.

If all poles are mechanically coupled to operate as one unit, a single common indicator is allowed.

Signaling the position: clause 5.104.3.2

The electrical signal from auxiliary contacts follows these rules:

• Neither the indication nor the signaling of closed or open may be given until the moving contacts have reached their closed or open position and clause 5.104.1 is met.
• A signal common to all poles is issued only if all poles have a position conforming to the above.

The definition of closed position (3.6.110) adds that the predetermined continuity means that the contacts are fully engaged to carry the rated normal current and the rated short-circuit current, as applicable.

How the position indicator is tested

Clause 6.105 applies when a position indicator is used instead of a visible isolating distance, and the details are in Annex A. It is an optional type test. It has two parts:

• Test of the power kinematic chain. The moving contact of the disconnector is blocked in the closed position, and the force or torque that the mechanism transmits when trying to operate is measured. Then a force of 1.5 times the measured value is applied to the chain, downstream of the opening point. In manual mechanisms, the force applied to the handle can be up to 750 N.
• Test of the indicator kinematic chain. It is made by blocking the indicator instead of the moving contact. No test is required if the indicator is marked directly on a part of the power chain. Nor is one required if the part between the two chains is inside an enclosure with a minimum degree of protection IP2XC that passed a 2 J impact test.

The test is passed if, at the end, the indicator still correctly shows the position of the moving contact and the indicator chain has no permanent deformation.

In the routine test, during the mechanical operations it is verified that the indicator correctly marks the open and closed positions.

Effect on other tests

• Dielectric tests in the open position are made with the minimum isolating distance at which the indicator or signaling can still give the open position, or with the minimum compatible with the locks of clause 5.104, whichever is smaller.
• When the design requires adjusting the indicator or signaling, the adjustment is made according to the instruction manual. No deviation of these devices is allowed in the dielectric and short-circuit tests.
• The mechanical endurance test verifies the specified operation of the auxiliary contacts and position indicators.

The interlocking that uses these signals is explained in mechanical and electrical interlocking, and its applications in the busbar disconnector and the line disconnector. The operation is covered in the motor-operated mechanism. The mechanical endurance of the disconnector is covered in M0, M1 and M2 classes of the disconnector. You can practice the order of operations with the interlocking table.

What not to do

• Do not take a position signal into an interlocking logic without checking that it comes from auxiliary contacts that follow the actual position of the contacts.
• Do not assume that the «open» signal and the «closed» signal are the negation of each other: the standard requires that each signal be given only when the contacts have reached their position. There is an intermediate state with neither.
• Do not remove or adjust the indicator without following the manufacturer’s manual: the standard requires no deviation in the tests.
• Do not rely on an indicator whose connection to the contacts passes through a force-limiting device.

What to request from the manufacturer

• The way the open position is indicated: visible distance or indicator, with its Annex A test report.
• The mechanical locks provided for the open and closed positions.
• The auxiliary contacts available and their relation to the position of each pole.

When to call us

At Tiza Group we test disconnectors in AIS and GIS substations and verify that the actual position of the contacts matches the local indication and the signal that reaches the control system and the interlocks. Field work is done in Colombia, or elsewhere on request. See our testing and commissioning services or write to us with your substation data and we will send a quotation.

Related guides

• M0, M1 and M2 classes of the disconnector
• Rated contact zone of a disconnector
• High-voltage disconnector: types, parts, classes and tests
• Disconnector motor mechanism: parts, signals and tests
• Interlocking: what it is, mechanical and electrical

References

• IEC 62271-102, High-voltage switchgear and controlgear - Part 102: Alternating current disconnectors and earthing switches, 2001 edition with Amendment 1:2011 and Amendment 2:2013, clauses 3.6.110, 5.12, 5.104.1 to 5.104.3.2, 6.102.3, 6.105 and Annex A.

Frequently asked questions