Insulator Locking Pin Testing Machine (Cotter Pin Tester) for Ball & Socket Couplings

Locking pin testing machine at a glance

• Purpose: verifies the locking system of insulator ball and socket couplings — the test that decides whether the locking pin stays in its seat under load.
• How it works: the tensile load is applied along the axis of the locking pin and is increased gradually until the pin slides out; the peak load is captured and displayed automatically.
• Standard: IEC 60383-1 (verification of the locking system), with the pin dimensions from JB/T 8181-1999 and the coupling dimensions from GB/T 4056-2008.
• Load range: 1 – 3000 N, indication accuracy ±1%, resolution ±500 000 digits, peak value recorded; maximum stroke of the pull-out pin 300 mm.
• Specimens: ceramic and glass disc insulators, one unit or two units in series, and the locking system of a single composite insulator.
• Coverage: pin designations 16, 20, 24, 28, 32 and 36; insulator units of 70, 120, 210, 300, 420 and 550 kN.

1. What this machine is used for

The locking pin — also called cotter pin or locking clip — is the small but decisive part of an insulator string with ball and socket coupling. It locks the connection between the insulator units and the metal fittings, and it prevents the coupling from sliding out of its seat. If it comes out, the string separates.

In IEC 60383-1 the corresponding sample test is the verification of the locking system: the locking pin shall withstand the specified tensile load applied along the axis of the pin without sliding out of the coupling.

On the CT-LP26 the load is applied along the pin axis and is increased gradually until the pin starts to slide, so the ultimate value is measured and recorded as the test result. The peak load is captured automatically and shown on the screen, so the sliding value is read directly without manual judgement.

2. Standards applied

• IEC 60383-1 – Insulators for overhead lines with a nominal voltage above 1000 V – Part 1: Ceramic or glass insulator units for a.c. systems – Definitions, test methods and acceptance criteria (verification of the locking system).
• JB/T 8181-1999 – Locking pins for ball and socket couplings of string insulator units.
• GB/T 4056-2008 – Connecting dimensions for ball and socket couplings of string insulator units.
• GB/T 1001.1-2003 – Ceramic or glass insulator units for a.c. systems – definitions, test methods and acceptance criteria.
• GB/T 19443-2004 – Ceramic or glass insulator units for d.c. systems – definitions, test methods and acceptance criteria.
• GB/T 19519-2004 – Composite insulators for a.c. overhead lines with a nominal voltage greater than 1000 V – definitions, test methods and acceptance criteria.

3. Technical parameters

An R-pin and a W-pin are loaded differently, and the machine covers both. For an R-pin a suitable device applies the tensile load along the axis of the pin on the eye of the pin; for a W-pin a rectangular steel bar of section F5 x T as specified in JB/T 8181 applies the load along the axis on the two arc ends of the W-shaped pin.

4. Key functions

• Load applied along the axis of the locking pin and increased gradually until the pin slides out of its seat, so the ultimate value is measured and not guessed.
• Peak load captured and displayed automatically – the sliding value is read directly without manual judgement.
• Both pin forms covered: the R-pin is loaded on the eye of the pin, the W-pin on the two arc ends with a rectangular steel bar of section F5 x T (JB/T 8181).
• Load indication accuracy ±1% over a range of 1 – 3000 N, with a resolution of ±500 000 digits.
• PLC with an all-in-one touch screen terminal: accurate counting, simple operation and the peak value shown on the screen.
• Protection guard and a complete safety control and protection system keep the operator and the equipment safe in all working conditions.

5. Typical applications

• Disc insulator manufacturers – sample test of the locking system of glass and porcelain disc insulator units.
• Composite insulator manufacturers – verification of the locking system of a single composite insulator.
• Electrical testing laboratories – type, sample and routine verification to IEC 60383-1.
• Power utilities – incoming inspection of the locking pins delivered with the insulator units.

6. Frequently asked questions

1. What is a locking pin and why is it tested?

The locking pin – also called cotter pin or locking clip – is the small part that locks the ball and socket coupling of an insulator string, so that the coupling cannot slide out of its seat. If it comes out, the string separates, which is why IEC 60383-1 has a sample test for it: the pin has to withstand the specified tensile load applied along its axis without sliding out.

2. How is the load applied to an R-pin and to a W-pin?

For an R-pin a suitable device applies the tensile load along the axis of the pin on the eye of the pin. For a W-pin a rectangular steel bar of section F5 x T, as specified in JB/T 8181, applies the load along the axis on the two arc ends of the W-shaped pin.

3. Which pins and which insulator units are covered?

Pin designations 16, 20, 24, 28, 32 and 36 as specified in JB/T 8181, which covers insulator units of 70 kN, 120 kN, 210 kN, 300 kN, 420 kN and 550 kN. Ceramic and glass units are tested one unit or two units coupled in series, and for a composite insulator the locking system of a single insulator.

4. Does the operator have to watch for the moment the pin slides?

No. The load is increased gradually and the peak load is captured and displayed automatically, so the sliding value is read directly from the screen without manual judgement.

5. What are the load range and the accuracy?

The measuring range of the load is 1 to 3000 N with an indication accuracy of ±1% and a resolution of ±500 000 digits. The maximum stroke of the pull-out pin is 300 mm.

6. What does the machine need to run?

AC 220 V at 1 kW, a working temperature from -20 °C to 50 °C, a stable 220 V a.c. supply and an indoor location with good ventilation. The machine occupies 700 x 700 x 1800 mm and weighs about 150 kg.

Related disc insulator inspection equipment

The dimensions of the same unit are checked on the deviation checking device for disc insulator units, the routine mechanical test is run on the routine tensile testing machine for disc insulators, and post insulators are checked on the post insulator deviation inspection platform. The complete range is listed under insulator test equipment.