Secondary-side leakage

Secondary-side Leakages also Affect the Primary Side... 

Why did we use the symbol Llk in the dissipation equation above Why didn t we identify it as the primary-side leakage ( Llkp ) The reason is that Llk represents the overall leakage inductance as seen by the switch. So, it is partly Llkp — but it also is influenced by the secondary-side leakage inductance. This is a little hard to visualize, since by definition, the secondary-side leakage inductance is not supposed to be coupled to the primary side (and vice versa). So how could it be affecting anything on the primary side ... 

In brief, the secondary-side leakage has created much the same effect as a primary-side leakage. 

When both primary- and secondary-side leakages are present, we can find the effective primary-side leakage (as seen by the switch and zener clamp) as... 

So, like any other reactive element, the secondary-side leakage also reflects onto the primary side according to the square of the turns ratio, where it adds up in series with any primary-side leakage present. 

The secondary side leakage (uncoupled) inductance is associated not only with the actual transformer windings, but the lead-out terminations and even the PCB traces leading to and... 

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. 

In high-power offline Flybacks, the trace inductances on the secondary side reflect on to the primary side, and can greatly increase the effective primary-side leakage inductance and degrade the efficiency. The situation gets worse when we have to stack several output capacitors in parallel, just to handle the higher RMS currents. Long traces seem inevitable here. This has been discussed in detail previously. 

However, the best method to measure leakage is actually an in-circuit measurement — so that we include the secondary-side PCB traces in the measurement. The recommended procedure is as follows. 

The parasitic capacitance between the primary and secondary windings transfers noise across the isolation boundary. Since the secondary side ground is usually connected to the chassis, this noise returns via the earth plane, in the form of CM noise. The situation is very similar to the tradeoffs required in heatsink mounting issues. In this case, we wish to couple the primary and secondary very close to each other in order to reduce leakage inductance (especially in flyback transformers), but this also increases their mutual capacitance, and thus the CM noise. 

There were investigated cases with or without cooldown by secondary side and with or without loss of primary cooling 5 t/h flow on each 6 MCP sealing (see analysis No. 10 and 11. in Appendix 4). In the cases without primary leakage the time available for recovery - even with secondary depressurisation - exceeds 10 hours. This time reduces to less than 5 hours without secondary bleed, if the pump seals are defected. In conclusion, the secondary bleed should be initiated if only a loss of primary coolant also exists. Otherwise the secondary side depressurisation can lead to shorter available time for recovery. 

An increase in radioactivity indicated by condenser air removal system monitors, and blowdown system monitors will reveal reactor coolant leakage through steam generators tubes to the secondary side. Routine analysis of steam generator secondary water samples will also indicate increasing leakage of reactor coolant into the secondary system. 

The detection of leakage across the steam generator boundary between the primary and secondary side is discussed in Section 5.2.5.1.3. Leakage across this boundary would be quantified, after the indication of radioactivity in the condenser, by monitoring the pressurizer level, along with the RCS makeup water requirements. 

Disturbances in the main heat transfer system Leakages and ruptures on the secondary side Steam generator leakages (water ingress)... 

The leakage inductance of both coils has been modeled by an inductor in series with the load, since the current in the coils also produces leakage flux. These inductances are labeled L p and Lj, respectively. Notice that the leakage inductance for the secondary side has been divided by the turns ratio n, squared because it was reflected to the primary side. Resistors labeled Rp and Rj have also been placed in series with the load to represent the resistance of the conductors used to wind the coils. Again, the secondary resistance has been divided by the square of the turns ratio, since it was reflected. 

The nonideal characteristics of a transformer include core and winding losses, presence of leakage fluxes, and finite permeability of the core. Hence, the actual model should include the physical representations of these nonideal characteristics. This is shown in Fig. 10.105(b), where the shunt magnetization and core loss components have been ignored for the sake of convenience. Such approximations are common in transformer analysis and only cause trivial inaccuracies in computation. Figure 10.106 shows the equivalent circuit of Fig. 10.105(b) with the secondary-side impedance referred to the primary side. 

Although the analysis demonstrates that no fuel rods are damaged, and that there is therefore no release to the reactor coolant, a conservative analysis has been performed assuming 10 percent of the rods are damaged. Activity carried over to the secondary side because of primary-to-secondary leakage is available for release to the enviromnent viathe steam line safety valves or the power-operated relief valves. The significant radionuclide releases due to the locked rotor accident are the iodines, alkali metals and noble gases. 

Turbine island vent discharge radiation monitor. This monitor measures the concentration of radioactive gases in the steam and non-condensable gases that are discharged by the condenser vacuirm pirmps and the gland steam condenser. This measurement provides early indication of leakage between the primary and secondary sides of the steam generators. The monitor provides alarm in the main control room. 

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