Contribution for new C62.69 clause Saturated Core Secondary Winding Parameters

Transcription

1 Mick Maytum 0-0 Contribution for PC.a Contribution for new C. clause -. Saturated Core Secondary Winding Parameters This contribution is set in IEEE Word template style to simplify its incorporation in an IEEE work product. The contribution author retains the copyright of the clause. material here and grants the IEEE a license to use and modify the clause. materials. Placeholders for the existing C. clauses, Figures and Tables have been inserted to maintain the correct numbering in clause.. Editing instructions are in bold italic font i.e. Insert and Change. 0. Overview. Definitions, symbols, acronyms and abbreviations Figure Symbol for a two winding transformer Figure Symbol for a two winding transformer with polarity indication Figure Symbol for a two winding transformer with electric screen Figure Transformer with center tapped windings 0. Surge parameters Figure Common-mode surge conditions for the transformer Figure Common-mode surge conditions for a transformer with an electric screen

2 Mick Maytum 0-0 Contribution for PC.a. Characteristics. Characteristic measurement Table Classification of microclimate conditions. Inter-winding capacitance Figure Test circuit to measure the transformer inter-winding capacitance Figure Test circuit to measure the inter-winding capacitance of a transformer with an electric screen 0. Insulation resistance (IR) Figure Test circuit to measure the insulation resistance of a transformer Figure 0 Test circuit to measure the insulation resistance of a transformer with an electric screen Table Typical test voltages. transformer voltage-time product Figure Test circuit to measure the transformer voltage-time product Figure Generator and transformer secondary voltage waveforms 0 0 Insert the following clause.. Saturated core secondary winding parameters.. General Under differential surge conditions, a saturating core signal transformer secondary winding surge current let-through is typically triangular with three phases: ) Transformer linear surge current transfer from primary winding to secondary winding, the current ratio being set by the transformer's primary to secondary turns ratio, n. ) Transformer core saturation event setting the peak secondary current, the event time being set by the transformer's Vs product for core saturation. ) Saturated core secondary winding energy dump, the current waveform of which is set by the transformer saturated core winding inductance, the peak secondary current, the secondary winding resistance and the secondary load impedance.

3 Mick Maytum 0-0 Contribution for PC.a Figure shows an example waveform with the three phases indicated. 0 A 0 A Phase ) Linear Phase ) Secondary winding energy dump 0 A Phase ) 0 A Core saturation 0 A 0 µs µs µs µs µs µs Figure Example waveform of transformer secondary winding differential surge let-through current During phase ), when the saturated core decouples the primary and secondary windings, the effective secondary circuit becomes the transformer saturated core winding inductance, L S(SAT), the established secondary current, I S, the secondary winding resistance, R S, and the secondary winding circuit load impedance as shown in Figure. R S I S L S(SAT) Secondary winding Secondary load circuit 0 Figure Effective secondary circuit after core saturation.. Purpose These tests measure the transformer secondary winding resistance, R S, and the secondary current decay waveform in phase ) Figure. From these two measurements, the effective transformer saturated inductance value, L S(SAT) can be calculated... Test methods... Secondary winding resistance, R S, test method A digital multimeter, DVM, having a resolution of 0. or better, can be used to measure the winding resistance. Figure shows the test circuit to measure the secondary winding resistance, R S, (a) and, if required, the primary winding resistance, R P, (b).

4 Mick Maytum 0-0 Contribution for PC.a Tx input Ethernet port magnetics assembly output W DVM a) Tx W DVM input Ethernet port magnetics assembly output Key T X Transformer or Ethernet port magnetics assembly incorporating transformer DVM Digital Multimeter or equivalent for measuring resistance Figure Resistance measurement of a) secondary winding and b) primary winding... Secondary current decay waveform test method b) Figure shows the test circuit used to drive the transformer into a saturated core condition. A./0-/0 combination wave generator, G, with a charge voltage of. kv will provide a current, I GEN, with a peak value of about 0 A into the input (primary winding) of transformer, Tx. The short circuit output (Tx, secondary winding) current, I S, waveform produced is measured and recorded by the current transformer, CT, and oscilloscope, O.

5 Secondary short circuit current, I S - A Mick Maytum 0-0 Contribution for PC.a G R GEXT W I GEN input Tx Ethernet port magnetics assembly IS output CT O./0-/0 0 Key T X Transformer or Ethernet port magnetics assembly incorporating transformer G./0 -/0 combination wave surge generator CT Current transformer or current probe O Oscilloscope or equivalent recording secondary current, I S.. Values Figure Test circuit for measuring secondary short-circuit current under surge conditions A pure exponential decay based on series inductance and resistance elements, having a time constant of L/R = L/R, decreases in amplitude by /e or 0. during a time period of L/R. This fact can be used to calculate L S(SAT) from the measured current decay waveform and the measured resistance value R S. Figure shows an example I S current waveform with a peak current of. A. The time constant period is best measured early in the decay when the current decay rate is most rapid, but not at the peak where there may be some aberrations. In this case the time period was measured from the 0 % amplitude value (. A) to the 0*0. =.% (. A) amplitude value. In this example the measured time constant period was µs. If the measured value of R S was, then the calculated value of L S(SAT) would be L/R *R S = * = µh % µs. % 0 0 Time - µs Figure Example I S current waveform

6 Mick Maytum 0-0 Contribution for PC.a 0.. Criteria Manufacturers could, if required, control the secondary winding resistance, R S, value in the same way as they control the primary resistance, R P, value for Power over Ethernet, PoE, applications. In practice, the impedance of the secondary load circuit is likely to make R S variations a second order effect. The value of L S(SAT) will depend on the transformer core and the winding arrangement. While the manufacturer can control the winding arrangement, the core saturation characteristic is not usually a key parameter as the core is selected linear transformer operation. Having an idea of the L S(SAT) value from these measurements enables the circuit designer to estimate the level of energy available to the secondary load circuit after core saturation.. Ratings Table Classification of microclimate conditions Table Impulse withstand test voltage for rated impulse voltage Change the previous clause Figure numbers in Figure labels and in body text as indicted below Previous Figure # Changed to Figure # 0

7 Mick Maytum 0-0 Contribution for PC.a Annex A (informative) Bibliography

8 Mick Maytum 0-0 Contribution for PC.a Annex B (informative)./0 Impulse