Fixed Electrolytic Liquid Starter

Hi All,

I'm looking for some information on fixed liquid starters for slip ring motors. The starter i'm dealing with is a 3 step with 2 banks of electrodes controlling the starting sequence of a 3-phase 315kw slip ring motor. First stage one bank is in series with the rotor windings, second stage two banks are in parallel and a final stage coupling contactor.

This is my first time working with such a starter and my knowledge of the operating principles of the system is limited. I'd appreciate if someone with some more knowledge than myself could explain these principles. I also have some specific questions i'd like to put out there.

* The starter hasn't been in use for some time and the electrodes have become slightly corroded, will this influence the starting characteristics of the motor?

* There are a total of 9 electrodes (all of equal area and all fully immersed in the electrolyte) per bank, 3 directly connected to each of the rotor windings and 2 parallel to each of the three rotor electrodes (1 either side each seperated aprrox 50mm from the central rotor electrode), these 6 electrodes are in turn coupled with copper busbar at the terminals above the tank. What is the purpose of the 2 electrodes either side of the individual rotor electrode?? Would 1 not suffice, i.e. a total of 6 electrodes per bank?? Does the capacitive element of the plates have any bearing??

* As mentioned the starter hasn't been in use for a few years. Will the solution which is still within the tank be usable or is it probable that it will need to be replaced. If the latter is true, what is the most commonly used electrolyte and what weighting of this vs. water should be used. Rotor current - 330amps, rotor voltage - 580 volts.

I'd be very grateful for some feedback.
Thank you.

Matthew.