Korndorfer starting 4

[jacphi]

we are using the Korndorfer starting method to start a 16000kw/13.8 kv motor by using three breakers. typical Korndorfer starting scheme has a start breaker,a shorting breaker and a run breaker. see link

http://www.seamanship.co.uk/engineering/EKsamplepages/Motor starters.htm

we are taking a deviation from the typical Korndorfer starting method by connecting the run breaker after the start breaker and leaving the start breaker on always. is there any problems in doing so?

 

[Marke]

Hello jacphi
Appart from the fact that there is voltage permanently on the coils of the transformer, I se no disadvantage of this operation. The voltage on the coils will not result in current flow as there is no voltage acros the coil, but there is voltage stress on the insulation.
Best regards,

Mark Empson

http://www.lmphotonics.com

 

[GGOSS]

Hello jacphi,

There are two control posibilities for Korndorfer connected auto-transformer starters. The operating sequences are;

Standard Korndorfer Control Scheme; Transformer line & star point contactors pull in together, time setting elapses, transformer star point contactor drops out, run contactor pulls in.

Enhanced Korndorfer Control Scheme; Transformer line & star point contactors pull in together, time setting elapses, transformer star point drops out, run contactor pulls in, transformer line contactor drops out.

In the Standard Korndorfer Control Scheme, a failed control connection to, or failed coil on the Run contactor would result in continuous current flow through the transformer. As transformers of this nature are generally only short term rated, exposure to current for extended periods will result in failure, unless of-course the transformer has fitted with thermistors to interrupt the control circuit when an over-temp condition is detected.

In the enhanced Korndorfer Control Scheme, the transformer line contactor drops out following energisation of the run contactor. This eliminates the problematic issues/possibility of transformer failure discussed in the previous paragraph.

Regards,
GGOSS

 

[jbartos]

Suggestion to jacphi (Electrical) Sep 21, 2003 marked ///\\we are using the Korndorfer starting method to start a 16000kw/13.8 kv motor by using three breakers. typical Korndorfer starting scheme has a start breaker,a shorting breaker and a run breaker. see link

http://www.seamanship.co.uk/engineering/EKsamplepages/Motor starters.htm

we are taking a deviation from the typical Korndorfer starting method by connecting the run breaker after the start breaker and leaving the start breaker on always. is there any problems in doing so?
///The modification does not change the functionality of the motor operation. I would not recommend leaving the start breaker always on since the current flows over two contacts in series in each line. This is wearing contacts of two contactors rather than one only. It is known that contacts have contact resistances (or impedances in general). This contact resistance elevates contact temperature (RI**2) and causes contact material changes in time, which degrade the contact quality.\\