SDG – Technologies

My LRS Is Experiencing trips

Question: We have an LRS installed for a 1MW crusher that is experiencing trips.


What about a soft starter solution? According to our understanding a soft starter will not be able to supply the required starting torque for this application?

What are the preferred starting methods for MV slip ring motors sized at about 1MW?

Answer: With a moving electrode type LRS, the starting torque can be very well controlled if the LRS is tuned correctly, die water temperature is well controlled and the electrodes are in a good condition.

Therefore any torque may be chosen, as hard or soft as needed. No other soft start solution is necessary.

However, other liquid starters are in use around the 1MW level, called Vapourmatic starters, that do not have a moving electrode but rather several fixed tanks. With these, the torque cannot be well controlled, in which case an upgrade to moving electrode LRS may be in order.

If you already have a moving electrode LRS (like the EPM1), we can test the LRS and tune the starter electrolyte solution for any torque you need. Crushers are typically started very often, leading to overheating of the water and subsequent tripping. In this case we can install our standard air-blast cooler to control temperature at a set-point.

If you need extended monitoring of the starter performance over a time period to find the root cause of the trips, we can install a portable (or permanent) recorder to monitor start-ups remotely in order to recommend the best solution or further fault-finding.

Some other factors that can influence a start-up of a crusher, are:

  1. The time it takes to complete the start-up cycle: if it is an EPM variable resistor starter, the cycle time might be too long. Crushers have less inertia and should start faster compared to mills and fans. Speed is also needed to give momentum for the crushing, should you need to start with ore in the crusher.
  2. Starting under load can cause tripping depending on the starting torque that’s been set in the starter (based on the resistance/conductivity of the electrolyte solution). The type of ore can be the determining factor so it is important to know what kind of ore is being crushed. If the ore is too hard (like chrome ore or magnetite), starting under load might not be possible, but with copper, gold and platinum it can be done. From experience we found that the starting torque need to be in the order of 180 – 200% of rated torque, when starting under load.


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