Hi jraef,
Thanks for the answers.
Surge arrestors for protection of LV motors are not installed on LV motors, but on LV fire pump controllers. This is required in NFPA 20.
You are right that fire pump motors are not switched on/off so oftern as the other motors. Our client insists on surge...
Hello everyone,
MV fire pump controllers use vacuum contactors to switching fire pump motors. Surge arrestors are normally required to protect motors from operation overvoltage when motors are stopped by vacuum contactors.
However, NFPA does not require surge arrestors on MV fire controllers...
Hi gentlemen,
Are surge arrestors needed to protect incoming cubicles and transformer or large motor feeder cubicles from switching overvoltage?
IF vacuum breakers are used,ABB 30kV and 6kV switchgear always install surge arrestors. But sometimes Siemens and Schneider do not install the surge...
Hi everyone,
We need to implement differential protection on a 30/6kV 15MVA transformer. Are the CTs for differential protection different from CTs for overcurrent protection? Can we use 5P20 xxx/5A CTs for differential protection? In which case shall we use PX or TP series CTs?
How to decide...
LionelHutz & Lionel,
Generally we soft start motor with 300% - 400% FLA to limit voltage dip. This is origial design. However, we have to challenge the limit of 200% FLA for this project. If unrealistic, then we try 250% FLA, but can not be higher than 250%. Even if the study shows that...
LionelHutz and jraef,
It is a pump, and the valve can be closed during start-up. We have not bought the soft-starter yet. We need to check feasibility.
We will provide all relevent data and ask motortronics to make a study before we can place an order. I also have concerns about long starting...
LionelHutz and jraef,
Thanks for the reply.
I agree that mechanical and piping system can also benefit from soft start and soft stop. On this project, the main reason for soft starter is to limit voltage dip on the bus during starting the big motor. If we can soft start the motor with a...
Hi everyone,
Our team is asked to start a 2.5MW/6kV motor with solid state soft starter. The motor is about 300m away from the electric room. The manufacturer of soft starter, Mototronics suggests that a large reactor shall be connected in the circuit to overcome dV/dt problems. I have concerns...
Hi,
I made mistake in reply. The starting current limit is 300% FLA, not 30%. Motor locked rotor factor is 6 times FLA. Soft starter is the type of phase-angle fired thyristor.
Then my transformer size is :
Starting voltage is about 70% rated voltage.
Starting kva = 70% . 2MW / 0.9...
Hi everyone,
We use motor starter c/w fused contactor to control 6kV motors. The 6kV motors and low voltageg 380V motors are all controlled by DCS system.
For the LV motors, smart or intelligent MCC are used,such as Siemens Smart Tiastar MCC.Each MCC cubicles are serial linked to an interface...
Thanks everyone for prompt reply.
Soft starter is c/w bypass contactor. Max starting time is 40 seconds.
K-rated transformer is expensive, and order of harmonics components is not easy to decided to choose K-factor. So I tend to specify a captive transformer.
The captive transformer is rated...
Hi everyone,
We will install solid state soft starter to drive 2MW 6KV motors. The soft starter will fed by 13.8kV switchgear via 13.8/6kV captive transformers.
The solid state reduced voltage starter switches on-off during starting and causes harmonic component in the network. I know VFD...
Hi Bill,
Sorry I was in a hurry yesterday and made mistakes.
The 60kV system neutral grounding resistor (NGR) is rated 200A 1s.
And the maximum fault level on the 60kV bus is 25kA.
We will use program such as ETAP to calculate grounding potential rise, step potential, touch potential...
Hello everyone,
We are doing grounding simulation and calculating grounding resistance, touch potential etc. The incoming 60kV step down to 5.5KV and the 60kv system is high resistance grounded and Neutral grounding resitance is rated 200A 10ohm 1s. The maximum fault level at 30KV bus is 25kA...
Thanks for all the reply.
We try to persuade the client to adop the option of fused contactor. However, client still stick on the circuit breaker-contactor because of 55 degree ambient temperature. CB is used to replace fuse,and no fuse will be installed.
I hope we can find vendor to supply...
Gooday,
We have a 30kV switchgear lineup with tied section A and B. The tie breaker is normally open. However, it will be closed for a paralled incoming operation not more than 20 seconds before switching for maintenance . The worst case of fault level on 30kV bus is parallel incoming...
Hello everyone:
We have a 3MW 5.5kV DOL - started motor installed in a concrete plant. The process designer says that it may be started and stopped several times a day. So contactor shall be used to start and stop it. However, the client requires that vacuum circuit breaker will be used to...
