This capacitance becomes part of our circuit that already includes cable inductance and resistance. Wye (Y) connection, also known as “Y” connection, is a three-phase circuit in which all the three loads are connected at a single neutral point. The presence of third (and other zero-sequence) harmonics at an ungrounded neutral can cause overvoltage conditions at light load. A corner grounded (delta) transformer is an industrial hack from the 1950’s. 2.38a and the transformer is assumed to be unloaded (load provides damping). Figure 5 shows a wye-delta grounding transformer with the primary grounded, connected to the secondary winding of the ungrounded wye-wye bank. Based on the definition, this is … wye ungrounded motor and wye-wye solidly grounded transformer secondary is also a part of the 480 V system. Where supplied by transformers if the supply system is ungrounded ... 4-wire and is wye-connected and the neutral conductor is used as a circuit conductor ... (secondary). A stabilizing resistor can be used to dampen out transients. Re: Ungrounded Vs grounded wye in transformer primary 03/16/2016 2:52 AM I think the short-circuit current will be divided-according to each path impedance-into 2 parts: one through transformer neutral and second to remote system neutral. This is a variation from the norm in metering electricity. Oh no! Ungrounded System Ground Fault Detection An example of an ungrounded system is shown in . To accomplish this with a delta secondary transformer, an artificial neutral must be created using a zigzag transformer. phase from leg to leg instead of the normal 120 recreating the proper voltages- but- the derived leg is wild, can run at 180-210 volts to neutral, even though the leg to leg voltage remains steady at about 240. In a wye connected HRG system, intermittent faults that cause so much trouble in ungrounded systems will be eliminated by the neutral system ground resistor because its insertion limits the total current flow to ground. Only 3 wires and no ground or neutral wire. The transformer primary is delta connected or in ungrounded wye connection, while the secondary can be either grounded or ungrounded wye or delta connected. Usually, the voltage transformer will be wye-grounded–wye-grounded and an auxiliary wye-grounded–broken-delta transformer will be used. Surge arresters are connected from phase conductor directly Very common. See Figure 1. In contrast, any grounding problem in grounding systems 2, 3, or 4 will not effect its respective primary grounding system due to its primary delta windings. This system is shown in Fig. If the source and load neutrals and ungrounded, the voltages would be the same as with grounded neutral EXCEPT when there is fault in the system. Electrically neutral is zero potential with respect to live potential. Figure 5 is simplified. When there is a line-ground fault on a wye-grounded source, voltages will be balanced for the most part. When there is a line-ground fault on a wye-ungrounded source, voltages will become unbalanced. Abstract: This paper documents the detailed analysis of the three-phase ungrounded wye-delta transformer bank serving a combination three-phase induction motor and single-phase lighting load. Ungrounded interconnection can be provided for inverter-based systems requiring it. 3 on page C20)? detecting and protecting against ground faults for an ungrounded system. 2 on page C20). If one conductor or the other is grounded, the system’s phase-to-ground voltage is 120V. Can detect both line and ground faults : Allows positive and negative sequence components For ungrounded systems, the greatest voltage between the given conductor and any other circuit conductor is also the phase-to-ground voltage. The special application discussed in this paper utilizes three element metering on an ungrounded or impedance grounded system. Ferroresonance may be eliminated by using a single primary wye with dual secondary VTs where one VT secondary set is wye connected and the other VT secondary set is a broken delta : Can only detect line faults. 13.8 kv Z winding - resistance grounded wye. For a single A disadvantage of the Delta center-tapped service transformer is the fact that it has a wild leg. Q1) Difference between ground wire and neutral wire? Such as the situation when a break occurs on one phase upline from the transformer. Specifically this includes ungrounded Delta, ungrounded wye and impedance grounded wye systems. It is always recommended that Wye Delta transformers be connected such that the Wye Primary is not grounded. Accounting; CRM; Business Intelligence This method of metering is applied to primary and secondary winding is the ratio and polarity. What's the secondary phase current for a 150kVA, 480V to 208Y/120V, 3-phase transformer (Fig. In a wye transformer, the 3-phase and single-phase 120V line current equals the phase current (I Phase = I Line) (Fig. ungrounded or high impedance power systems. Figure 1: Distributed cable to ground capacitance can be drawn equivalently as a wye connected capacitor at the output terminals of the upstream transformer. ii. This is a very important distinction to make and keep in mind as we go through the analysis. Any grounding problem in the secondary of Tl will effect the 480 V system. Disadvantages of Delta-Delta or Ungrounded Wye-Delta Connection: i. Utility-side SLG faults are difficult to detect. Some styles failed to load. iv. This allows for one transformer stock to cover both 277/480 grounded wye customers as well as 480 volt customers seeking an ungrounded system. operate on ungrounded systems. Secondary grounding is irrelevant from primary grounding. However, with an ungrounded Wye Delta connection it is possible to back feed significant voltage when one primary phase is opened. You would have a higher step-down voltage with a Wye secondary because its line-to-line voltage encompasses two phases with a 120-degree angle between them. A 3/spl times/3 transfer function matrix is developed that makes it possible to determine the load line-to-line voltages with a knowledge of the primary voltages of the transformer bank. Ungrounded systems have the secondary windings of the distribution substation transformer connected either in ungrounded delta or ungrounded wye, with the former connection being more common. primary is hooked in delta, secondary in wye and grounded. Voltage protection on ungrounded systems requires a connection to three phase instrument voltage s transformer (VTs). Let's apply this to an actual problem. Utility arresters are subjected to high steady-state over-voltages if islanded on an SLG fault. The secondary side of the three phase VTs are s connected together in a broken-delta configuration, and two wire leads are brought to a single overvoltage relay. A Delta secondary is better for stepping down voltages than a Wye. Secondary can either be center grounded, corner grounded or ungrounded. The two 4.16kv windings feed two ungrounded 4.16kv buses (radial feed). Wye current and voltage calculations. The wye-delta grounding transformer allows the flow of the exciting current triple-harmonics, thereby achieving a sinusoidal flux wave and inhibiting the triple-harmonics of the line-to-neutral voltage. Grounding of a Wye transformer Secondary. A classic example is an 12kv ungrounded delta line. 1. Wye transformer The grounded wye primary/open delta secondary has 60 deg. Sometimes the main voltage transformer will have a double secondary, one of which can be connected to the broken delta. The distribution feeders are three-wire three-phase and two-wire single-phase circuits. •Either winding can be left ungrounded, or grounded at any point without affecting the grounding or the voltage of the other winding. On a 480V, three-phase, 3-wire, ungrounded delta system, the phase-to-phase voltage is 480V. The secondary windings of the transformer are connected in delta configuration and the system feeds an ungrounded load. System 3 has an ungrounded single-phase transformer secondary, and System 4 has a grounded wye transformer secondary. Using sequence components terminology this is can be stated that the zero-sequence circuit of the delta-wye-grounded transformer is open. Transformer with Ungrounded Secondary: ... has a delta primary then the currents would circulate in the delta windings and no current would flow in the secondary wye-grounded circuit. Secondary and low side (and LV) terms are used interchangeably; ... that a HV Wye-grounded transformer connection has different voltage and current characteristics compared to the HV Wye-ungrounded or a HV Delta connection during an open phase condition. ANS) Neutral wire is a return path for unbalance current. Figure 1 below. Unlike delta connection, wye-connected systems carry a fourth neutral conductor, often grounded but sometimes left floating (ungrounded wye system). This is a very unusual setup to the best of my knowledge in that ungrounded systems are normally fed from delta-transformer windings. When constructing a Y-Y transformer using single-phase transformers connected in a bank, the measured line-to-neutral voltages are not 57.7% of the system phase-to-phase voltage at no load but are about 68% and diminish very rapidly as the bank is loaded. Zero- Open Source Software. Please try reloading this page Help Create Join Login. 2 x 4.6 kv X and Y windings- UNGROUNDED WYE. System 2 has an ungrounded delta transformer secondary, and an ungrounded single-phase transformer primary. The only thing different is the transformer secondary is wye and left floating rather than delta; everything else is exactly like an ungrounded delta. The NEC still requires that the grounding electrode conductor be sized to the secondary ungrounded conductors. When installing a new system, ie the y secondary of a transformer, we run a #6 ground wire to building structure, drill and tap a hole and bolt a lug to it. The analysis of an ungrounded Wye-Delta transformer bank serving aninduction motor and single-phase lighting loads February 2000 IEEE Transactions on Industry Applications 36(1):39-45