Disconnector Assigned Contact Zone (xr, yr, zr)

Short answer

In a split-support disconnector, the moving contact is on the device and the fixed contact is mounted elsewhere: on a flexible conductor or on a rigid busbar that moves. The contact zone is the set of positions the fixed contact can occupy while still engaging correctly with the moving contact (IEC 62271-102, clause 3.5.110, edition 1.2, 2013).

The manufacturer declares the assigned values of that zone, written xr, yr and zr (clause 4.102). The manufacturer also declares the angular displacement the fixed contact tolerates. The user has the opposite job: to make sure that, in service, the fixed contact never leaves those limits.

Which disconnectors it applies to

The assigned contact zone is required only for split-support disconnectors (clause 4, list of ratings). The standard gives the pantograph and semi-pantograph disconnectors as examples. It also applies to earthing switches of that construction. On the high-voltage disconnectors most installed in Latin America: Hapam, Coelme, MESA and Siemens 3DN disconnectors.

For other disconnector types, the standard does not include the contact zone among the assigned values.

The three movements of the fixed contact

The standard describes what moves the fixed contact in each direction. The description changes depending on whether the contact hangs from a flexible conductor or sits on a rigid busbar:

For flexible conductors, the standard also distinguishes two vertical values: z1 for short spans and z2 for long spans. The reference tables start at 72.5 kV. Table 1 is for fixed contacts supported by flexible conductors and Table 2 for rigid conductors. Both are for guidance only.

What the user must ensure

Clause 4.102 sets a clear condition. When specifying the substation design and the bending strength of the insulators, the user must ensure that the fixed contact stays within the declared limits, taking the service conditions into account.

Clause 8.102.3 also asks the user to check three effects that add to the conductor’s own thermal expansion and wind load:

• Longitudinal displacement from wind on other connected components and from movement of the equipment.
• Perpendicular deviation from wind forces on other connected components and from movement of the equipment.
• Vertical deviation from other loads hanging on the busbar and from the loads imposed by the operation of other equipment connected to it.

If the sum of these movements exceeds xr, yr or zr, the disconnector may close badly. The fixed contact ends up outside the reach of the moving contact.

How it is verified: the contact zone test

Clause 6.102.2 defines a type test to demonstrate the operation of split-support disconnectors at the different positions of the fixed contact within the assigned zone. With the device open, the fixed contact is placed at the extremes of the zone. It goes first at the maximum height declared by the manufacturer and at that height minus zr. Then it is moved to each side, horizontally and longitudinally, by half of yr and half of xr. At each position the disconnector must close and open correctly.

In the other type tests, the vertical position of the contact within the zone is chosen to represent the most unfavorable condition. If in doubt, the test is repeated at the highest and the lowest position. The short-circuit test report must describe how the fixed contact was mounted on the upper conductor.

What to ask the manufacturer for

• The assigned values xr, yr and zr, and the tolerable angular displacement of the fixed contact. In the tender, the standard requires the manufacturer to state the assigned contact zone for split-support disconnectors (clause 9.102.1).
• The type test report, with the way the fixed contact was mounted in those tests.
• The bending strength of the insulator and the height of the terminal above its top, which enter the calculation of the forces.

What to include in your inquiry or order

Clause 9.101 lists what the person inquiring about or ordering a disconnector must state. Several items relate directly to the contact zone:

• The required contact zone, if applicable.
• Whether the conductors connected to the disconnector, or to which the separate contact is mounted, are rigid or flexible.
• The mounting conditions and the high-voltage connections, for example the hanging arrangement of the fixed contact, and whether the supporting structure is supplied with the equipment or not.
• The rated static and dynamic terminal loads (clause 4.103).

Clause 8.101 adds that, when selecting a disconnector, the static and dynamic terminal loads at site that result from the substation design and the use of rigid or flexible conductors must be considered.

What not to do

• Do not take the values of Table 1 or 2 as the assigned values of a specific device.
• Do not accept the zone based only on conductor expansion. Add the wind and the loads of the other connected equipment.
• Do not change the conductor type, the tensioning or the fittings without repeating the zone check.
• Do not apply this zone to a disconnector that is not split-support.

Related topics

The contact zone is one of the mounting conditions the disconnector shares with its earthing switch. The drive that closes the contact is explained in the motor operator of the disconnector. The conductor forces on the equipment, which depend on the same connection design, are covered in mechanical terminal loads of an instrument transformer. Before operating the disconnector in the bay, review the line disconnector interlocking.

The mechanical load the conductor applies to the terminals is covered in mechanical terminal load of a disconnector, and the disconnector position in disconnector position: locking and indication. The M0, M1 and M2 classes of the disconnector complete the mechanical ratings.

The other parts of IEC 62271 are laid out in the standards for primary equipment testing.

When to call us

At Tiza Group we check with you that the connection of your disconnectors respects the declared contact zone, from bay design through commissioning. See our testing and commissioning service, available in Colombia or elsewhere on request. Write to us and we will send you a quote.

Related guides

• Mechanical terminal load of a disconnector
• Disconnector position: locking and indication
• Disconnector classes M0, M1 and M2
• Earthing switch: classes E0, E1, E2
• Disconnector motor operator: parts, signals and tests
• Hapam, Coelme, MESA and Siemens 3DN Disconnectors

References

• IEC 62271-102, High-voltage switchgear and controlgear - Part 102: Alternating current disconnectors and earthing switches, 2001 edition with amendments 1 (2011) and 2 (2013): clauses 3.4.102, 3.5.110, 4.102 (Tables 1 and 2) and 6.102.2.

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