Case Study on Importance of Relay Co-ordination in Process Industries

Relay Co-ordination

Hello Everyone

I am sure many of Electrical Engineers would have witnessed such inadvertent tripping in their Cement plant, Steel plant, fertilizer plant or other Industries.

Case Study on Importance of Relay Co-ordination in Process Industries, Here the case is a Cement Plant (But such things happens in another type of industries also)

–      Such cases happen in majority of industries and it’s not that their Protection system are not Co-ordinated, issues lies in day by day change in Electrical system. Below Case Study will ask you to beware while changing your Electrical Distribution System.

–      Clinker Hammer Crusher Motor Tripped in Overload due to Jamming. After 30 seconds Control room gave a command to start the crusher again, as due to heavy starting torque the jamming can be cleared (As it has been done many time before), But when the given command to crusher motor, the whole plant tripped.

–      As the Clinker crusher Jamming happens at least 3 to 4 times in a year and the plant was running since last 4 years, such co-ordination problem never happened?

–      We were called for trouble-shooting the above; as this was happened 2nd time in last 3 months. The first thing we did was to check whether the complete Electrical system is co-ordinated or not? We found that the system was co-ordinated since commissioning stage and they had the records of that.

–      Next things we ask their team any modification done in the distribution team like changing of existing motor with less KW or adding any extra load on that MCC due to any process requirement.

–      Yes they Said, One 37 kW old Compressor was removed due to no usage and one 180 kW compressor was shifted from another MCC to this MCC (As the load on that MCC was around 100 %) and one more 75 kW High Pressure Pump (Used for breaking Jamming in Kiln) was installed as per requirement of Process / Production. So a total of around 217 kW was added, and they have manually adjusted the setting accordingly of MCC incomer and PCC outgoing Panel.

–      Now actually what happened that Clinker lump came and Clinker crusher motor was tripped (According to them this happen 2-3 times in a year), so they started again after 30 seconds, but as the whole plant was already running except clinker crusher. So when the commands come for starting, MCC was already at 80% load and when the 315 kW motor started the Starting current was obviously to be around 4 to 5 times of Motor FLC, the total current cross the threshold of that relays which they forgot to change the setting, of 6.6 kV Side as mentioned in SLD, that made the complete PCC bus dead, and the total plant was completely tripped and it took around 2 hours to start back. It was a 5000 TPD Plant, this breakdown cost the plant around 410 Tonnes of Clinker which is approx 500 Tonne of Cement i.e 10000 Bags of Cement which means around 25 to 28 Lacs in just 2 hours (Total of 50 – 55 Lacs for 2 Breakdown). And all that modification which was done to improve stability and efficiency has gone to dust in just 2 hours.

–      But ideal condition should have been that MCC-6 Incomer should have tripped, Not Motor because Motor started normally with just extra load on it.

Solution to above

Circuit Breaker Maintenance

–      Every time any big Modification is made to the Electrical distribution system, your complete Relaying and Protection should be co-ordinated again to avoid such huge loss.

Where System Protection can be of help:

We can provide complete relay co-ordination of your plant. We have done that in many industries (Private and Government).

For Relay Co-ordination Inquiry Please send it


System Protection

Electrical Relay Testing Services

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