Grounding switch for GE switchgear SECOGEAR

The GE SECOGEAR series medium voltage armored switchgear adopts JNH1/4 type grounding switch from domestic 12/24/40.5kV to IEC 17.5/27/36kV.  

This grounding switch is different from JN15 clamp type moving contacts, but uses contacts installed at the static end, and the moving blade is only a copper bar, which means that the static contacts are exactly opposite to JN15. The disc spring has high stability, high contact pressure, and high mechanical strength of the welded spindle. Real short circuiting copper bars, rather than thin-walled copper pipes, with the actual materials clearly visible at a glance.

JNH type grounding switch 17.5kV 31.5/40kA applied to SECOGEAR-17.5kV switchgear for maintenance in front of the cabinet

The grounding switch has passed multiple KEMA type tests.

The JNH4-17/50 50kA grounding switch adopts a cast integrated cylindrical contact finger, a plum blossom static contact, and the plum blossom contact is uniformly stressed, with strong resistance to neutral and short-circuit closing. After a short-term withstand test, the blade type contact makes it difficult for the grounding switch to quickly separate after welding or heating, resulting in a significant increase in operating force. In contrast, the plum blossom contact type static contact grounding switch does not change its opening operating force.

Conduct dynamic thermal stability and short-circuit closing tests at KEMA.

Although the appearance of the grounding switch looks the same, there are differences in specific materials and processes. The production process and hardness of the static contact, the thickness of the short connecting tube, and the diameter and force value of the spring all differ. It is necessary to ensure that the closing and operating force meet the requirements, and the mechanical life passes the test. Therefore, the design needs to be considered as a whole.

Regarding the closing of the grounding switch, many customers require E2 level 5 times of closing. The closing test is conducted at rated voltage, and the closing short-circuit current is 63/80/100/130kA. The main factors affecting the closing ability are:

Closing speed

A fast closing speed can reduce the erosion of pre breakdown contacts and shorten the arc time. The closing speed of 12/24kV is 4-5m/s, while the closing speed of 40.5kV grounding switch needs to be increased to 6-7m/s. Therefore, three springs are required, and a large spring sleeve and small spring structure are needed.

Contact shape

Adopting circular and rod-shaped static contacts with uniform electric field and good shape for moving contacts, the electric field is evenly distributed to reduce electrical breakdown distance.

contact material 

Similarly, contacts with strong erosion resistance can also reduce erosion, especially for high voltage switches such as 40.5kV and above. Using copper tungsten arc contacts or copper tungsten alloy as contact heads can also reduce erosion.

The contact has a magnetic locking plate, which clamps the contact under the action of short-circuit current.

Contact pressure is a key indicator for determining the thermal stability of a grounding switch. Calculate the contact resistance based on the contact pressure to calculate the voltage drop at the contact connection, and determine whether the contact will be melted under thermal stability based on the voltage drop. The impact of contact pressure on closing is reflected in the fact that the contact can quickly stop after closing, without rebounding and causing erosion. The use of disc spring contacts provides high pressure, stability, and small size.

The requirement for neutral contact in closing is very high. Skewness and neutral deviation can cause the contact to burn out and burn severely on one side, affecting the subsequent closing.

Connection arrangement

The connection arrangement involves the direction of electric force during closing. If the direction of electric force is favorable for closing, it will accelerate the closing speed and reduce erosion. Otherwise, it will reduce the closing speed and increase the contact erosion time.

The characteristics of GE switchgear are genuine materials, sturdy and durable, which will not reduce product performance and reliability due to high cost. The products of the engineering project are consistent with the prototype of the type test, and cannot be changed arbitrarily. The grounding switch has stable performance, and although the operating force is large, its reliability and safety are higher.