Secondary winding

Chills, fever, slight sweating, aversion to wind. Secondary symptoms... 

If possible comparisons are focused on energy systems, nuclear power safety is also estimated to be superior to all electricity generation methods except for natural gas (30). Figure 3 is a plot of that comparison in terms of estimated total deaths to workers and the pubHc and includes deaths associated with secondary processes in the entire fuel cycle. The poorer safety record of the alternatives to nuclear power can be attributed to fataUties in transportation, where comparatively enormous amounts of fossil fuel transport are involved. Continuous or daily refueling of fossil fuel plants is required as compared to refueling a nuclear plant from a few tmckloads only once over a period of one to two years. This disadvantage appHes to solar and wind as well because of the necessary assumption that their backup power in periods of no or Httie wind or sun is from fossil-fuel generation. Now death or serious injury has resulted from radiation exposure from commercial nuclear power plants in the United States (31). 

The six secondary phases are obtained by shorting the centre points of each of the three-phase windings of a 3p transformer secondary. 

The accuracy of a VT depends upon its leakage reactance and the winding resistance. It determines the voltage and the phase errors of a transformer and varies with the VA on the secondary side. With the use of better core material (for permeability) (Section 1.9) and better heat dissipation, one can limit the excitation cunent and reduce the error. A better core lamination can reduce the core size and improve heat dissipation. 

It is possible to have two windings in the secondary circuit of a VT when it is required to perform the functions of both measurement and protection. 

These are single-, double- or three-phase wound-type trans-formers with windings on both primary and secondary sides (Figures 15..3(a) and (b)). 

When the primary of a three-phase two-winding transformer, having its secondary wound for a three-phase open delta, is connected across an unbalanced supply system, a residual voltage across the open delta will appear. This is the principle on which this transformer is based (Figure 15.4(a)). As discussed in Section 21.2.2, and illustrated in Figure 21.7, the phasor sum of all the three line to ground voltages in a three-phase balanced system is zero, i.e. 

When this balance is disturbed, due to either an unbalance in the loads or due to a ground fault, a residual or zero phase sequence voltage in the neutral circuit will appear. When one of the phases in the secondary of a three-phase transformer is open circuited and a three-phase supply is applied to its primary windings, there will appear... 

Residual voltage The residual voltage appearing across the secondary windings will be three times the zero sequence voltage, if it is found in the primary... 

Wherever two separated secondary windings are provided, say, one for measuring and the other for protection, the markings will indicate all such details as are marked against (a) for each secondary winding. 

Xi - Secondary winding reactance referred to the primary side Z- Load (burden) impedance /nf Excitation or no load current... 

Maximum resistance of the secondary winding corrected to 90°C or the maximum operating temperature considered. In fact, it should be substituted by the actual operating temperature. 

The limiting secondary resistance is required to determine the secondary limiting e.ni.f. which is = (FS) x rated secondary current x VA X resistance of secondary windings at 90°C or the highest operating temperature as in Table 14.5, where... 

Figure 15.35 Single and three-phase VTs with one and two windings in the secondary...

CT with a primary winding (4) CT with two secondary windings, in 2 sections which may be each with its own magnetic core, connected in series or parallel... 

Power frequency withstand test on secondary windings... 

The secondary windings should be capable of withstanding a rated power frequency, short-duration withstand voltage of 3 kV for I minute, (iii) Power frequency withstand test between sections... 

This lest is applicable when the CT s primary and secondary windings have two or more sections. Then the section in between will be capable of withstanding a similar voltage as noted in item (ii) above. 

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. 

Consider tertiary and secondary windings with a higher BIL. if possible. 

Generally, an arrester on the primary should be adequate to protect the secondary windings. When it is not, a separate arrester may be provided between each phase and ground of the secondary windings. 

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