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Zero sequence current transformer Installation - Electrical industry

10kV Neutral low-resistance grounding system in big cities generally used on the electricity grid. Transformer substation , Opening and closing station 10kV zero-sequence protection device using extrinsic zero-sequence current Transformer Use more and more, as in the past limited the use of zero sequence current transformer, so found a number of installation problems, and some even result in zero sequence ground fault protection device refused to move in to protect the leapfrog.

1 installation problems (1) zero sequence current transformer to be installed in the switch cabinet floor above, should be reliable bracket. However, some factories or construction units will be zero sequence current transformer installed in the switch cabinet bottom bracket below, what is more tied to zero sequence current transformer in the cable, which runs counter to the principle of fully enclosed switchgear is neither safe, no dust, but not anti-small animals, leaving a lot of hidden dangers.

(2) Cable Terminal through the extrinsic zero-sequence current transformer, the cable metallic shield grounding line and the zero sequence current transformer outside the laws relative position is not correct. According to "of Beijing Electric Project to install a point of order, "states: three core Power cable Office of the metallic layer of the terminal must be well grounded; Plastic Shielded copper cables per phase and the steel armor shall be ground tin solder (oil impregnated paper insulated and sheathed cables should lead pack welding ground), cable through the zero sequence current transformer, the cable metal sheath and ground response in isolation, cable access location (cable grounding wire and cable joints of metal shield) the following in the transformer, the grounding wire should be connected directly to ground (see Figure 1); take place over the transformer, the grounding wire should be grounded through the transformer (see Figure 2), ground wire must be connected to the switching cabinet for ground copper rafts, grounding wire shall be stranded copper or tinned copper braided wire, grounding wire cross section must meet the regulations requirements. During the inspection, discovered that some cable grounding line of the zero sequence current transformer to wear when not wearing, some should not wear a zero sequence current transformer overturn wearing, causing the accident ground zero sequence protection can not function properly.

(3) Cable Terminal done as relatively large, resulting in current transformer magnetic circuit is not closed. The commonly used three-core 10kV power cable cross-linked polyethylene cable, cross section more to 240mm2, 300mm2, thick cable diameter core plus three additional hot melt sealant gloves even more crude, zero sequence current transformer sets do not go up, construction on the open interfaces of zero sequence current transformer, cable cover over the interface but forgot to recovery; some recovery, but the interface to restore strict; more of the terminal separately from the first three core zero sequence current mutual inductance device diameter crude has just stuck in the middle of zero sequence current transformer interfaces the zero sequence current transformer can not be resumed closed, resulting in zero sequence current transformer magnetic circuit is not closed and can not work properly.

(4) contiguous zero sequence current transformer secondary is open in the cable construction work to resume after the end of not timely, resulting in current transformer secondary open circuited.

(5) Cable Shield Grounding line of welding wire is not grounding terminal Terminal Also not connected to the switch cabinet to set the ground copper rafts, but the casual lap bolt on the switch cabinet.

2 correct construction methods 10kV line protection device with external zero sequence zero sequence current transformer attached, in the design and construction should be noted:

(1) shall ensure that use of zero sequence current transformer Cable Terminal diameter greater than the outer diameter;

(2) Do not dismantled as far as possible the construction of zero-sequence current transformer, such as to be dismantled, the work must be the end of restitution;

(3) grounding wire shall be stranded copper or tinned copper braided wire, grounding wire cross-section should not be less than 25mm2, grounding terminal ends must be welded, and correctly handle the grounding line and the zero sequence current transformer the relative position of grounding line must be installed in ground copper rafts;

(4) to zero before power sequence protection system tuning to ensure the protection of working.
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