Bad 3 Phase Transformer. The uneven torque results in abnormal noise and vibration in motor. RE: Transformer blows primary fuses with no load. I may not get anywhere near the 4,000 and 2,500 amp sources I have coming in but mine is rock solid everywhere except for one time in a corner area of a warehouse, there was a blown fuse on one leg of a stepdown that slightly upset the balance. For loss of one primary fuse (say yours) you will lose power the other two phases will see a reduction of about 13.4% in their service voltage. To observe the components in the magnetizing currents and induced voltages for di erent con-nections, with and without the neutral being connected. All the padmount transformers involved in this case study were 5 legged core construction. (Fuse) = (I*250%) next size smaller if primary current is 9 Amps. To connect three single-phase transformers in (a)Star/delta(Yd1, Yd11) (b)Star/Star(Yy6) and to obtain the no-load line voltage ratios and phase relations for each connection. The working theory is that either … A short between the two multiplies the current flowing BACK through the fuse of L1. Number of breaker operations that occurred when transformers with different fuse ratings failed. Fuse rating = 2000 x 250 / 1.732 x 415 = 696 Amps. Single Phasing of Induction Motor – Causes The single phasing of induction motor can occur because of causes external to the motor which are. Area Fuse sizes used Number of breaker operations Number of transformer faults 1 20 A 11 11 2 20 A 3 3 3 20 A 8 8 4 8 A 1 18 5 8 and 20 A 12 61 6 20 and 8 A 28 65 Table 2. In order to reduce the power loss to the distribution end, the power is transmitted at somewhat higher voltages like 132 or 400KV. However after the transformer The red phase is not showing regular 120/208 red readings. steven. When ONE fuse of a three phase circuit blows, you should normally: Change the ONE fuse that blew Change all THREE fuses Change the ONE fuse plus the next upstream fuse (same phase) Change all THREE fuses plus the next upstream fuses Comments and opinions are always encouraged. The transformer is a 67kV/12kV 10000 kVA unit. Transformer Primary Fuses Blown Transformer Primary Fuses Blown cslater (Structural) (OP) 29 Mar 11 23:48. Category Science & Technology; Show more Show less. 3 Answers. • 3-phase transformer banks can introduce a phase shift between the three-phase primary and the three-phase secondary – function of the primary and secondary winding connections . The table below gives the commonly encountered problems in 3 phase squirrel cage induction motors, cause of problems and what remedy to apply to bring the motor back to production. The single phasing of three phase induction motors forms the most common hazard to motor operation, because of the possibility of overheating and burning-out of the motor under this condition.. Calculate Size of Circuit Breaker or Fuse on Primary and Secondary side of Transformer having following Detail Transformer Details(P)= 1000KVA Primary Voltage (Vp)= 11000 Volt Secondary Voltage (Vs)= 430 Volt Transformer Impedance= 5% Transformer Connection = Delta / Star Transformer is in unsupervised condition. Therefore, 250kVA transformer can be charged with the 710A fuse. OUTPUT FUSE = 1*125% next size higher if secondary current is 9 Amps or higher. Joined Dec 3, 2011 Messages 2 Helped 0 Reputation 0 Reaction score 0 Trophy points 1,281 Activity points 1,305 My first post here, might be a stupid questions, sorry if it is. In the case of circuit breakers, the immediate answer is to find the breaker that has tripped and reset the lever to the ON position. fuse and arrestor blew when third cutout was put in. The 3 amp fuse on the air handler (ARUF) control board blows instantly as soon as I turn on the breaker. Hence the nearest available size of the fuse is 710Amps. Primary and Secondary Fuse Recommendations for all Three Phase Transformers Fuse = I*125% next size higher if primary current is 9 Amp or higher. Fuse ratings must consider the possibility of nuisance trips if the rating selected is too low for all possible operating conditions. 2. You will complete three-phase transformer bank diagrams for open Delta-open Delta, open Wye-open Delta systems. Fig. You are going to like this answer! The motor will run but would not be able to drive rated load. Since one of the phases is now disconnected, current through other two phases will increase to produce the desired torque. Three phase transformers are used to step-up or step-down the high voltages in various stages of power transmission system. 3 - phase bank kvar system voltage 2.4/4.16kv system voltage 7.62/13.2kv system voltage 15.2/26.4kv 150 25t – – 300 50t 15t – 600 100t 25t 15t 1200 – – 25t table 6: transformer fusing – 15.2/26.4kv transformer fuse links – overhead fuse links – underground kva 1 phase kva 3 phase pads full load amps jea item id chanc Top . For Three-phase transformer, Transformer fuse rating = 2000 x S (kVA) / (1.732 x V (V-L)) Example: Calculate the fuse sizing of the 250kVA, 415 V three-phase transformer. One fuse is blown and the white tube is hanging down. The fuse goes even when no heat is requested. Per NEC, a larger primary fuse may be used to reduce nuisance tripping. The result of a phase loss is not intuitive. Three-phase electric power is a common method of alternating current electric power generation, transmission, and distribution. Three phase fuse failure relay is intended for continuous monitoring of potential transformer fuses. Joined: … We are in a factory and the main feeder transformer is defective. The concern of unbalanced voltages in a three-phase system must be considered when selecting fusing for power transformer protection. This is one of the most common transformer application questions. The red fuse in the switch gear is fine (checked between red and black and got 600, checked between red and ground and got 347v - standard voltages. The results of a phase loss depend on which phase is lost. If you can confirm the transformer size, maybe we can make some suggestions on the fuse size. rogerg Post subject: Re: Replacing a Blown Fuse. In electrical distribution, a fuse cutout or cut-out fuse is a combination of a fuse and a switch, used in primary overhead feeder lines and taps to protect distribution transformers from current surges and overloads. Oncor’s three-phase padmount transformer purchasing specification requires 4 or 5 legged core design in order to reduce the probability of tank heating when zero-sequence voltage is applied. No secondary fusing required. I agree it appears to be a corner grounded system. The power generated at various generating stations is in three phase nature and the voltages are in the range of 13.2KV or 22KV. Loading... Autoplay When autoplay is enabled, a suggested video will automatically play next. Count 3 fuses for a 3-phase and 1 fuse for a single-phase power supply. The transformer does not have any real load on it just 24v control for the relay and main contactor through 2 buttons it also powers a 24v coil on a solenoid do i need to fuse the secondry side of the transformer . THE "FLOATING NEUTRAL" BENEFIT. So often, this type of fuse blowing occurs maybe one time out of 5 or one time out of 10. The secondary side of a transformer refers to low voltage side of the transformer. A utility transformer at our site was brought online a few days ago and blew all three line side fuses after about 10 minutes. Calculations: Transformer Primary Current (Ip)= P/1.732xVp Transformer … … or higher. transformer blowing fuses. Also to prevent back-feeding the line when a line becomes de-energized, or to prevent backfeeding the hi side of the transformer if the fuse becomes blown. Inrush current can vary significantly depending on instantaneous value of the voltage (voltage phase angle) when the transformer is energized. If the transformer is a SolaHD T5H series the tap is full capacity, but we must define what full capacity means on one phase of a three phase transformer. Thread starter barsukas; Start date Dec 3, 2011; Status Not open for further replies. to prevent balance or bank action - to prevent burning out the two remaining transformers when on fuse blows and creates an open, the bank continues to provide 3 phase power using two transformers instead of 3. This will change if the transformer is an ungrounded Wye (3 wire) on the primary side. Dec 3, 2011 #1 B. barsukas Newbie level 2. We have 600v Red black blue for phases. Blue phase is the blown fuse in the switch gear. You only need two current transformers to monitor the power in a 3 phase, 3 wire system. 2:06. Secondary fusing is required. I've disconnect the C and Y terminals on the air handler control board plus the CNT terminal which goes to the contactor without help. All this assumes the three phase transformer is a 4 wire grounded Wye connection on primary and secondary sides. The possibility of one or two fuses blowing must be reviewed. They may exist, but I have never seen one. Single Phasing a case when any one phase out of the three phases fails. this panel has a 240/400v transformer on the primary and 24v on the secondry I have fused the primary side with a 4amp fuse on each phase . I'll try what you said micro mind thanks . Posted: Mon Aug 03, 2015 2:48 pm . 3. As far as marking, I have never seen a corner grounded system where the grounded conductor was identified as required by the rules in 200.6. The ampere rating of a primary-side protective device selected to accommodate the total loading requirements of two or more transformers would typi- cally be so large that only a small degree of … wye point not grounded. With individual fuses on each phase, it is just three, single phases (120deg from each other in order), so when L1s sinusoid is swinging negative, L2 is still in the positive. Eaton’s Cooper Power series Bay-O-Net fuse offers a protection package for single- and three-phase transformers. See chart for size. Use a fuse size based upon the results using the National Electric Code standards as a guide. Older homes and buildings may still use fuses instead of circuit breakers, which you can use to tell if you have a single or 3-phase power supply. Chamberlain, SD 3. The "fix" is to reset the breaker lever to the ON position or replace the blown fuse. Another thing that can cause this (and go unnoticed) is a 480: 208Y/120 or 240 transformer that has a fuse blown on one of the three phase input legs. a blown fuse on the transformer primary The quotient determines the percentage of amperage a fuse needs to be smaller than the VA rating of the transformer. The assembly combines the ease of hotstick operation with the safety of deadfront construction and is used with an isolation link to prevent line personnel from closing into a fault when replacing a blown Bay-O-Net link. Selection Guide for Transformer-Primary Fuses in Medium-Voltage Industrial, Commercial, and Institutional Power Systems I GENERAL mended-each transformer should be individually pro- tected. … When a fuse blows, a metal filament inside the fuse has burned through, meaning that you'll need to replace the fuse with a new one. In a previous module you have already covered the Wye/Delta bank and discovered that this bank has a characteristic of its own. Answer Save. The monitoring relay is used for continuous monitoring of fuses against blowing out or inadvertent removals and may cause incorrect tripping. It is a type of polyphase system and is the most common method used by electrical grids worldwide to transfer power. The service fuses for your main power supply are usually located in your fuse box or mounted near it. It is rather confusing, and rather deadly. I have a Honeywell HZ322 zone controller. 7200 floating high side. Reactions: micromind. 1: Three basic components found in a lightning flash [1]. energizing a 120/240 wye/delta bank. It was brought online unloaded and none of the secondary relays tripped. 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