В рекомендациях от Siemens пусковые сборки для фидеров звезда/треугольник идут с тепловым реле. Автоматический выключатель без тепловой защиты (только от к.з) + тепловое реле.
Я же сторонник использования автоматов с тепловой защитой, чтобы не использовать тепловое реле.
А как считаете ВЫ? Что «лучше» использовать для пусковой сборки звезда/треугольник автомат с тепловой защитой или автомат с к.з. + дополнительно тепловое реле.
На сайте Siemens есть короткая статья почему лучше использовать тепловое реле,
но эти аргументы для меня не убедительны.
https://support.industry.siemens.com/cs ... 0&lc=en-WW
3RA1: What is the best motor protection in a star-delta starter?
QUESTION:
Is it enough to rely on a motor protection circuit breaker or is a separate overload relay required after the line contactor in a star-delta starter?
ANSWER:
If only one motor protection circuit breaker without an additional overload relay is used in a star delta starter, the following disadvantages must be taken into consideration:
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a)
The actual rated current of a motor winding is only 58 % of the rated motor full load current. During start-up in star-mode this winding is protected by a motor protection circuit breaker that can allow 173 % 'overcurrent' for the winding without tripping! This is not sufficient and can lead to a burnt out motor if the event of a YD-time relay failure.
An overcurrent relay installed behind the line contactor will protect the motor in star- AND delta mode.
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b)
All 6 conductors to the motor have to be rated for 100 % motor full load current. If an overcurrent relay is installed after the line contactor all 6 conductors running to the motor may be rated for the set current of this overload relay (Ie motor x 0,58). The cost savings for cables are almost in every instance higher than the purchase price of an overload relay.
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c)
An additional overload relay behind the line contactor facilitates the discrimination between a short-circuit trip and an overload trip. A RESET button on the panel door allows the machine operator to reset an overload trip only in order to restart the machine again.
A circuit breaker handle however would allow the machinist to switch the circuit breaker into an existing short-circuit. This is not a good idea taking the wear and tear only of the circuit breaker into account.
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