Vsd Frequent Bursting Of Semiconductor Fuse

Dear Friends,


I have a problem with an obsolete Analog Four Quadrant DC Drive (Anti Parallel full wave 3 phase Thyristor Bridge), 90 Kw, 440 Volts, 60Hz.

The drive is employed in Rubber Tired Gantry Crane. The problem is the frequent bursting of 2-355 Amperes of semiconductor fuses.

Bursting of fuses happened intermittently, we decided to replace all the SCR modules as maybe the caused of such problem, but the semiconductor fuses is still blowing after few hours or after a day of operation ( although the cooling system is working fine)

No other option to try since we do not have any related technical documentation available, neither a piece of control cards (regulator, synchro, absorber or firing card).

One thing I noticed is the Incoming voltage supply to Drive, I got a balance of 440 phase to phase voltage and 257 volts potential to ground for each phases which is a normal value.

However, upon powering the drive, it comes out with unbalance ground potential for each phases. Say, R-Ground is 245 volts, S-ground is high as 300 volts! T-ground is 220 volts. Phase to Phase voltage is still balance on this case at 440 volts.

Is the circuit considered unhealthy on this case? Is this unbalance ground potential may cause high current and blows the semiconductor fuses? It seems Phase T leaks to the ground whenever powering up the drive. What is the relevant issue for this scenario?

I am not so familiar with VSD’s, I will appreciate anybody’s view and advice, an apology for this rashly done topic.

Thank you and regards to all viewers.


Gerry

2-dc Motor In Series Connection

Dear Friends,

We have 2 identical -5hp, 220Vdc Separately Excited Dc motor. Each motor is connected to individual- identical gear boxes but sharing a common load via shaft linkage for Crane Traversing application.

The 2 motor armatures are in series connection powered by dc variable speed drive, each field winding is in series connection feed with fix voltage from the same VSD. Basically the system is Base Speed only, Variable Armature Voltage at constant field current. The System is running well with this arrangement.

During our Periodic Maintenance, I’ve tried to release the load of both motors by disconnecting the coupling from gear boxes, the idea is to check the individual motor speed rotation without any load on it. To my surprise, motor rotation is not balance, one Motor Armature voltage is higher than its counter part.

Particularly, at low supply voltage of 60 Vdc drive output (low speed reference to the drive), one motor is notably rotating faster than the other one, I measure each armature voltage, Motor A takes 60 Volts while Motor B is almost Zero volt, stalled and humming! By increasing the speed reference to VSD, Motor B starts to rotate but the speed/voltage is not synchronized with respect to Motor A.

Both motor is sharing the same load via mechanical shaft linkages, if the Armature Voltage or Speed of this 2 motors are not equal, Motor A tends to overload and may fails sooner? Motor B with slow speed may become additional load of Motor A?

For 2 identical motor impedances connected in series, do I expect to get a balance Armature Voltage? Comments are very much appreciated.

I apologize if the question is appropriate.


Best Regards,

Gerry

Transformer Scr Arrangement For Vsd

Hello,

Greetings to Everybody!

I have an inquiry about the arrangement of Transformer for our 12 pulse Thyristor-DC Variable Speed Drive for Crane Application.

The Main Power line to our Rail Mounted Crane is from utility supply of 6.6 Kv 50 Hz.Transformer feeding the drive is 600 KVA,6.6 Kv 50Hz Delta Connection Primary, Secondary side got 2 winding arrangement, WYE and DELTA connection at 460 volts each, this transformer is feeding 2 individual DC drive, WYE for Drive A and Delta for drive B.The DC output of this 2 drives is in parallel connection controlling the 370KW DC Hoist motor.

I have a situation here, our crane was relocated wherein there is no utility power available and thereby needs to condemn the existing 600 KVA, 6.6 Kv Transformer and feeds the Crane from diesel generating set 1250 KVA 50Hz,460 Volts.Unfortunately we do not have a 6.6 Kv Generator.We use 1250 KVA capacity to feed other motors and auxiliary power.

The question arise is the original power arrangement of the Drives. Do we need to install a new 1:1 ratio Transformer 600KVA,460 volts with 2 individual-Wye and Delta winding arrangement to supply the drives ? or can we just directly supply both drives from our 460 V, WYE winding generator set???

I will appreciate advice and recommendation which may assist us technically, can anybody recommends a reference about Transformer?... Cheers for this great and valuable site!


Best regards,

Gerry

Thyristor Cross Reference

Hi,

I'm looking for a Cross Reference of obsolete high power SCR.This is manufactured by HITACHI: Type CJ02Y

I do not have a data sheet for this SCR except the following information:

C: Thyristor
J : 200 Amps rated current
02: Supplier process code
Y : 1400 volts

I intend to replace it with any other brand available in the market, unfortunately I can not compare some important specifications such as the "gate" current and voltage requirement to fire the SCR.

I will appreciate your kind assistance and its a great pleasure to know somebody out there who is willing to share their knowledge and expertise.

Best regards,

Moises