IEC 62505-3-3:2009 pdf download – Railway applications – Fixed installations – Particular requirements for a.c. switchgear – Part 3-3: Measurement, control and protection devices for specific use in a.c. traction systems – Single-phase inductive voltage transformers
4service conditions
Where the equipment described in this part of the standard is mounted on circuit breakers toIEC 62505-1, then the service conditions of that standard apply. Where they are separatelymounted and are used in association with switchgear then the same service conditions as theswitchgear apply.
5 Characteristics and use
The voltage transformer shall be:
a) either mounted inside the circuit breaker specified in IEC 62505-1; technical requirements of this IEC 62505-3-3 apply together with the construction and test requirements (asapplicable) of IEC 62505-1;
b) or separately mounted, free standing; technical requirements of this IEC 62505-3-3 apply.
6 Rating and design requirements
Clauses 5 and 6 of lEC 60044-2:1997 apply with the following exceptions:
– ln subclause 5.1.2 the following shall be added at the end of the subclause:
The secondary voltage values of 100 v or 110 V shall be preferred.
The rated ratio is given by the primary nominal voltage, as defined in lEC 60850，dividedby the rated secondary voltage.
ln Clause 6 the entire subclause 6.1.1 shall be replaced by:6.1.1 Rated insulation levels for the primary winding
Voltage transformers covered by this standard shall have the same insulation ratings andtest values as the equipment into which they are installed.See Table 1 of lEC 62505-1and lEC 62505-2.Free standing voltage transformers shall meet the same requirements.Subclause 6.1.5 of IEC 60044-2 is valid unless inconsistent with 9.1 of this InternationalStandard.
7Withstand conditions
The following requirements, additional to those of lEC 60044-2:1997, apply:
7.1 Primary side
The voltage transformer shall withstand the overvoltage characteristics described inlEC 60850,Annex A.
NOTE These events occur often and special attention should be paid to protect these voltage transformers.7.2Secondary side
The voltage transformer shall withstand the current produced in secondary winding for 1 s,when its terminals are short circuited.The primary voltage shall be Umax2 for this condition.where no Umax2 value is specified，Umax1 shall be used.
8Ferro-resonance
8.1General
The following requirements, additional to those of lEC 60044-2:1997, apply:
The structure of railwayelectrification network may easily generate ferro-resonancephenomena.They occur mainly in 25 kV,50 Hz systems.
When specified by the purchaser, the voltage transformer connected directly to the overheadline shall have the following characteristics in order to avoid the generation of ferro-resonancephenomena and withstand the overvoltages caused by the same.
8.2Prevention of the generation
The following features shall be adopted:
– minimum resistance of the primary winding: shall be specified by the purchaser;NOTE Typical resistance values are between 15 kQ and 50 kQ.
– flux density such that at Umax2(see lEC 60850) the saturation point is not reached.8.3Prevention of damages in the voltage transformer
The following features shall be adopted:
ability to withstand without damage on the primary side a voltage wave obtained bysumming a sinusoidal wave at rated frequency with a square wave at 1/3 of the ratedfrequency, with a total peak value of approximately 1,6× Un;
suitability to operate continuously at 1/3 of the rated frequency and rated voltage;- voltage factor of 1,9 (1,9 x U, for 8 h at rated frequency).
8.4 Ferro-resonance withstand test
The voltage transformer will be considered suitable to withstand ferro-resonance if thesecharacteristics are checked and tested， as a special type test named ferro-resonancewithstand test.This consists of a temperature-rise test at rated voltage, rated burden and 1/3of rated frequency. The standard temperature rises shall not be exceeded.
Particular design and construction characteristics
The following requirements,additional to those of lEC 60044-2:1997, apply:
9.1 Pollution
The dust pollution on railway tracks (e.g. in tunnels and at the seaside) is often higher than onhigh voltage transmission lines.For this reason the creepage distance shall not be less thanindicated in lEC 62497-1,Table A.7, for the appropriate pollution degree.
NOTE For the choice of the appropriate pollution degree， the degrees used in the associated switchgear (seeiEC 62505-1 and lEC 62505-2) should be taken into account.
