Protection surge transferences

The need to protect a rotating machine from switching surges, contact bouncing and surge transferences 17/576... 

These are only basic guidelines. It is difficult to define exposed or shielded equipment accurately. Equipment installed indoors may never be subject to lightning strikes or their transferences, but may be exposed to severe switching surges and require surge protection as for an exposed installation. There is no readymade formula by... 

The front of the transferred surge will, however, be less steep and dampened than on the primary side due to capacitive dampening. But sometimes this may also exceed the BIL, particularly of the tertiary (if provided) and also the secondary windings of the transformer, as well as the cable and the terminal equipment connected on the lower voltage side. This is especially the case when the primary side voltage is very high compared to the secondary. Protection of the secondary windings, in all probability, will be sufficient for all the cables and terminal equipment connected on the secondary side. 

The terminal equipment connected on the secondary side of the transformer is thus automatically protected as it is subject to much less and attenuated severity of the transferred surges than the secondary windings of the transformer. Nevertheless, the BIL of the interconnec-ting cables and the terminal equipment must be properly coordinated with the BIL of the transformer secondary, particularly for larger installations, say, 50 MVA and above, to be absolutely safe. Example 18,2 will explain the procedure. 

Surge protection on HV side is adequate to absorb direct surges. The transferred surges from HV side to the LT side are too feeble to cause any harm. In case of static switchings, on LT side, however, spike arrester will be essential. Section 6.14.1. 

We have considered protection of both 400 kV transformers, one for primary traiismission and the other for secondary transmission. We will now analyse the influence of surge renections and transferences of a surge occurring on the 400 kV primary transmission bus as shown in Figure 18.25 and its effects on segments A and B. 

Where a loading system s emergency shutdown system closes a valve on gravity or pipeline fed transfer systems, care should be taken to ensure the line is protected against pressure surges or hydraulic hammers which may cause gasket blowout or line failure (NFPA 30). 

Guo HL, Wolfe D, Epperly MW et al. (2003) Gene transfer of human manganese superoxide dismutase protects small intestinal villi from radiation injury. J Gastrointest Surg 7 229-235 discussion 235-236... 

CBl and CB2 were opened in the substation where Line 1 and Line 2 were charged from the other end in Figure 6.10. When DSl (or DS2) was opened (or closed), relay (for 66 kV line protection equipment) malfunction occurred, and no CB was tripped. The surge was transferred through the control cable via a CT. As a countermeasure, the CW control cable (without a metallic shield) for the CT circuits was replaced by a CWS control cable (with a metallic shield) with grounded ends. Then, the frequency of the malfunction decreased. Ferrite cores were also installed at the secondary circuit of an internal auxiliary transformer for the CT. No malfunctions occurred after this countermeasure. 

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