Figure 1 shows a common setup where three incandescent lamps are used to monitor the three phases: If there are no earth faults on the system all three lamps will illuminate at the same brightness. An open Y-∆ connection requires only two phases plus the neutral on the primary side of the bank in order to develop a three-phase voltage at the. Each transformer is rated as 10 kVA (current rating is 10 A and voltage rating is 1000 V). Since the phase sequence is R → Y → B, therefore, the direction of voltage from R phase towards Y phase is positive (+), and the voltage of R phase is leading by 120°from Y. 173 kVA Select from the following choices Choose the correct. Ex. If it still measures approximately zero, adjust the rheostat to minimum resistance and measure the 3 secondary line-to-line delta voltages. 5 with three cases:POCO could have unbalance primary voltage, bad regulation/tap changer and it happens to be on the line that derives the high leg - especially with an open delta primary configuration. When completing a meter ing test, remember that the V AB voltage leads the I A current by 30 degrees for a power factor = 1 condition (ABC phase rotation). Three-phase power is linked in a delta configuration. or. 2 Value of the DC-current of measurement 38 A 3. SEL recommends grounding the B-phase near the relay location for safety purposes , as shown in Figure 1. If it still measures approximately zero, adjust the rheostat to minimum resistance and measure the 3 secondary line-to-line. 73 times greater than the neutral to the hot leg voltage. Ohm’s law states that for some devices there is a relationship between electric potential difference, current, and resistance. 56. 577. delivered to the drive. A), voltage inputs (100-150 V),. The topics covered in this post are. User manuals, specification sheets, CAD drawings and more. Notice that the B-phase secondary is grounded. The voltage of the delta winding will be 63. The safety advantage of fused leads is that if a short occurs through the insulation of a lead to ground, the fuse in theApplications of the Open Delta or V-V Connection. ]. C phase to ground you have 480V. Calculating Power in Balanced Delta Three Phase Circuits _____ 21 3C1. PΔ = 3VI. Ohm’s Law. Delta wiring forms an equilateral. The floating Vn wire is just to show that the primary is delta only, neutral is not used. A low free-energy complex model. Figure 2 Phase-to-phase voltages in open-delta PT connection with IA as reference at power factor = 1 (ABC phase rotation) The relay calculates the actual phase- to-phase voltages , as follows:. The applied test voltage is raised in steps, 0. 6 Interpretation of the measured values 36 3. Quickly commission new controls with a minimal number of simple settings. The open delta voltage transformer configuration consists of two (2) double bushing VTs connected as shown in Figure 1. 120/240 V 3 phase is a red leg delta system. When measuring winding resistance, the reading should be observed and recorded once the resistance value has stabilized. 13(A). Limits and precautions. We have two existing PT's connected in open delta (connected line to line (A with B) and (C with B)) to a transmission line but we need to measure the line to ground voltage of all three phases. Determining self-discharge involves making just two open-circuit voltage measurements, but one must consider relaxation and voltmeter accuracy when grading cells. It is preferred that these data are free of measurement noise and bias. However, these models are not fully developed to a complete bus admittance matrix form, which can be readily used. Easy-to-use feeder protection and innovative features like SEL’s Best Choice Ground Directional Element logic and SELogic control equations provide superior protection on utility and industrial power systems. Voltage between three Phases = 240V (3-Φ). c. Then, place the two leads of the meter on either side of the load. In Gatton Substation, grid voltage steps down from 33 Corresponding author Yong Li is with the College of Electrical and Information Engineering, Hunan University, Changsha 410082, China (e-mail: yongli@hnu. g. 4A × 10Ω = 4 volts. The number of turns also gets reduced by 42 % of the number of turns in delta connection. 3-pound (16kg) panel is. Broken delta provides 3V0 only. The Ground fault protection system scheme uses over voltage relays and open break delta transformers. The terms line current and phase current follow the same logic: the former referring to current through any one line conductor, and the latter to. The power_compensated example uses a Multimeter block to measure the voltage across the secondary winding of a Saturable Transformer block and the currents flowing through two Series RLC Load blocks. Connecting the probes without ground lead to the individual phases should be safe (though with limited common-mode rejection ratio), as long as you observe the overvoltage category rating of both the probes and the scope. If a 50kΩ resistor was connected in series with the instrument during the test, determine the value of the unknown voltage. For example, if each transformer has a rating of 100kVA, then the kVA rating of the open delta. The observed frequencies are subdivided into various groups: alpha (8–13 Hz), beta (13–30 Hz), delta (0. Resistor damps only unbalanced situations. (Motor drive inputs are more likely to use a 4-wire system. In Digital Phosphor Oscilloscopes (DPO), the Z-axis can be. The purpose of the open-circuit test is to determine the no-load current and losses of the transformer because of which their no-load parameters are determined. initialized to 0. 32 kVA. L b a s e = 2161 2 π 60 = 5. and voltage measurement. Chaniotakis and Cory 11 +-R1 R2 R3 R4 Vs AB. In the case of the open delta configuration, by regulating two phases by +/-10% with regulators, the third phase is also regulated by +/-10%. Ex. Existing approaches include using downstream measurements to estimate tap positions of open-delta regulators [69] or using a voltage sensitivity-based approach to estimate excessive tap changes. I asked them to take voltage readings between phase-phase and phase-ground just to make sure it is an un-grounded delta secondary. 0 software. Open-Delta Step Voltage Regulator (SVR). Making differential voltage measurements is another means of reducing noise in analog input signals. Image used courtesy of Amna Ahmad. As a temporary measure, when one transformer of a delta-delta bank is damaged and removed for maintenance. In a secondary connected delta, winding current multiplied by __?__ is equal to line current. The polarity does not matter. Single-Phase Generators – for smaller single-phase loads, these gensets usually do not go above 40 kW. Any fault involving earth results shift of Neutral voltage. 1) This is a typical delta to wye configuration. This is a measure of the voltage applied to the detector to amplify the small circular dichroism signal. Accommodate wye-, delta-, or open-delta regulator configurations. mA = Milliamps. 28775 Aurora Road Cleveland, Ohio 44139 (440) 248-0400 Fax: (440) 248-6168 WHITE PAPER Achieving Accurate and Reliable Resistance Measurements in Low Power and Low Voltage Applications Low voltage measurements are often associated with resistance7 Expt-4: Determination of phase and line quantities in three phase star and delta connected loads 12-14 8 Expt-5: Measurement of three phase power using two wattmeter method. Typical Setting: 5% with 1 Sec TD 100 % Stator E/F Protection This is how we can obtain the three different voltages for this system; however, we can also have a corner-tapped Delta configuration. Voltage fluctuations measured by the EEG bioamplifier and electrodes allow the evaluation of normal brain activity. is often used in high-impedance grounded systems and U 2n = 110 V in effectively grounded systems. 4. The basic design topology of the VFD with a diode bridge, DC bus capacitors and insulated gate bipolar transistor (IGBT) output has proven to be reliable and beneficial from application and financial perspectives. +-Open Access Article This Open Access Article is licensed under a Creative Commons Attribution-Non Commercial 3. Now with V R4 having 4 volts dropped across it, the voltage difference between points C and D will be 4 volts as: C = 8 volts and D = 4 volts. R 0 is not required to be precisely this value since the equations are valid for any R 0; however, a Ro value in this range should. For typical delta/delta systems, the ratio is 2:1 — but for typical delta/wye systems, the ratio is 4:1 (Fig. What is the apparent power of this load? V = 415. slavag (Electrical) 6 May 08. The high leg is a nominal 208V to ground. the two between which is the ground tap). That’s why, The open delta will only deliver 57. 3v of the actual voltage measured with a standard voltmeter (I used an Astro AI DM6000AR). You can do that with a two-step. 5 Definitions of voltage, current, resistance. This solution eliminates the need for the CT which. 1a). [See Section 450. In CV, a linear sweeping voltage is applied to an aqueous solution containing the compound of interest. 2KV to 480V delta delta transformer, through the main switch gear breaker, which feeds all the 1600A feeder breakers. line 3: the standard definition of dc voltage “vdd!” line 5: definition of a voltage source at the input node A. They are mostly based on analysis of frequency components of voltage in open delta VT connection or phase currents and voltages. We also discuss when the two-wattmeter method. Because the unit for current is ampères, or amps, the symbol for it is A. 1 above). 1. Sigma-Delta ADCs. A voltmeter V , shown in the circuit, is used to measure this voltage and if suitably calibrated may be used to measure the zero-sequence voltage. Use line a as the common potential point. In Gatton Substation, grid voltage steps down from 33 Corresponding author Yong Li is with the College of Electrical and Information Engineering, Hunan University, Changsha 410082, China (e-mail: yongli@hnu. Hence the power-handling capacity of a open delta (V-V) circuit (without overheating the transformers) is 57. Delta-OCV is. 2) Delta Closing- Type DAC. The utility may be providing an Open-delta or an open-wye on their side, but it is definitely 3-phase. 2. Notice that the dc voltage value is set to the variable “vs” as defined in line 2. Then we would say the length of the paper is 11. g. Capacity of open delta system = √3 x rating of one transformer = √3 x 5 KVA= 8. Connected Delta. The Wye Connection – Phasor Addition. 400V and “3U0” will then be 1200V. VA – VN = 120∠30 (ABC), 120∠–30 (ACB) VB – VN = 0 (ABC and ACB) VC – VN = 120∠90 (ABC), 120∠–90 (ACB) Using these voltages with a balanced three. PΔ = 3VI. Once you have both the current and voltage, multiply them to obtain the power output. The ATPOL 8. 577 (or 57 . (open) leg at an angle other than 120 degrees. 577 (or 57 . The second secondary core is intended for a residual voltage measurement utilizing open-delta connection on 100:3V (approximately 33. Kirchhoff Voltage Law: Vin-Vout – VRʼ – VLʼ=0 Kirchhoff Current Law: Iin – Iout – Icʼ – IGʼ=0 ]. 100 KVA d. Where: V L is the line-to-line voltage, and V P is the phase-to-neutral voltage. or. As a rule, this voltage is 1,73 times higher in the case of an earth fault than the phase-earth voltage in the fault-free network - Both together: some protection devices use both the phase-to-phase voltages as well as the voltage. 869 kW, 9. The word "open" can get confusing for some people at times when dealing in electrical. At the most basic level, an oscilloscope's graph of an electrical signal shows how the signal changes over time (Figure 2): Figure 2: X, Y, and Z components of a displayed waveform. With the power off and the primaries still wye connected, open the delta and reverse the connections for one of the secondaries, but leave the delta open. The residual voltage of a system is measured by connecting the secondary windings of a VT in ‘broken delta’ as shown in Figure 4. The open delta or V-V connection is used to produce three-phase power using two single-phase transformers. If you are talking of stepping up in the sense of Generator Step Up Trafo, then one most say it is Star Delta Transformer as in Transformer we always need to mention HV winding side connection first and in GSUT,. This runs well as a three phase transformer but would have a power rating only 1 3 of that of three transformers connected into one ∆- three phase unit. Connected to a numeric. A 3-wire 120/240v load must not connect to the high leg, but only to the two 120v phases and the neutral, as with a 120/240v 1ph system. If it still measures approximately zero, adjust the rheostat to minimum resistance and measure the 3 secondary line-to-line delta voltages. Discussion of how the three phases are still produced in an open Delta transformer. The connectors of this amplifier are always insulated safety banana jacks (red/black). Any two legs will give you the phase to phase voltage either 208 if it's a "Wye" transformer or 240 if it's a "Delta" connection. Current is the rate of flow of charge, and voltage measures the energy transferred per unit of charge. 1 Cell measurements The cell inputs feature a scaling of approximately 0. High-precision battery cyclers can maintain constant currents with very little variation and can measure and store voltage and current with very little measurement. When using an ammeter or a voltmeter, you will notice that these usually have buttons or dials to choose the range of. This is because a line toVoltage, also known as electric pressure, electric tension, or (electric) potential difference, is the difference in electric potential between two points. Choice of MV LV transformer Electrical Installation Guide. Other types of three-phase supplies are wye connections, ungrounded delta connections, or corner-grounded delta ("ghost" leg configuration) connections. Therfore a voltage measurement from A-phase-to-ground is in phase with the primary VAB, and C-phase-to-ground is in phase with VCB. Also, recall that phase difference between Line current and Line-Line voltage (phase to phase voltage) is 30°. When you need to measure higher voltages, the PT reduces the measured voltage to that suitable for the voltmeter. 2n. Below is a diagram of the open delta connection used in medium voltage measuring circuits. In a Delta Connection, we get only a single. These characteristics cause errors in the measurement; refer. Voltage across open (missing transformer) was pretty off maybe 10--15%. 7 Examples 36 3. 7% of the power of a conventional transformer. in distribution networks is used and its winding tap is grounded to change the zero sequence voltage measured by the open delta voltage transformer for distribution networks. The Delta Pro supports up to 1600W of solar input from a variety of panel makers due to the wide voltage range (11-150V) it supports. A 3-wire 120/240v load must not connect to the high leg, but only to the two 120v phases and the neutral, as with a 120/240v 1ph system. 0V OPTION 1 NOTE: FILTER, FERRITE BEAD are optional OPTION 2 SN6501 (Transformer Driver) 5V_CNTL GND GND_ISO TLV70450 (5. plus or minus 0. PT-Name Plate Specifications. The utility company says it is an un-grounded delta secondary at 480V/3-phase/3-wire system. They are characterized by low short circuit voltage and low nominal. In the solutions presented in [8–13], the Wavelet analysis for various wavelet. Figure 2 Phase-to-phase voltages in open-delta PT connection with IA as reference at power factor = 1 (ABC phase rotation) The relay calculates the actual phase- to-phase voltages , as follows:. edu. If the system is utilizing wye-connected PTs, the voltages measured are in phase with the individual phase voltages. Impacts of measurement accuracy, sensor sampling frequency, and missing data on. Study with Quizlet and memorize flashcards containing terms like equal to the voltage from line to line, 1. Measuring 3-phase, 3-wire system with 2 voltage channels and 2 current channels (2V2I) Motor drives often use 3-wire outputs which can be accurately measured by using just 2 voltage and 2 current channels on the oscilloscope. What is usually used in high impedance grounded systems is broken delta (three transformers). 2. rsd =0 L1 L2 L3 Open delta winding for ground fault. Traditionally, the NVD protection signal has been derived from a star-connected set of capacitor bushings on the 33kV side of the transformer, feeding into an Edgcumbe. The secondary windings of a transformer with voltage ratings of 120/240 volts must be connected in series to supply 208-volt, 3-phase power on a 4-wire service line. In this application, an open delta PT connection is used to detect zero-sequence voltage at the generator terminals. 65,740/1,000=65. 577 x 30 kVA= 17. The components to set up the circuit are cheaply available relative to VFDs. - Measurement at the open delta winding: Here, the displacement voltage is determined directly by the measurement. X1, X2, and X3) are open-circuited when the three exciting current measurements are performed. Now you still measure 120 volts from line to neutral from either line, but from line to line where you previously read 208 volts, you now read 120 volts because the phase angle has been changed. The tan delta numbers at the higher voltages are compared to those at lower voltages and an analysis is made. Adjusting the signal to cover most of the display vertically makes for the best voltage measurements, as shown in the figure below. Sigma-delta (Σ-Δ) ADCs offer multiple benefits when designing RTD systems. 6. This voltage-dependent PFM approach later evolved into switching spectroscopy PFM (Box 2)—an effective tool for two-dimensional (2D) nanoscale mapping of the local switching characteristics 19. 2 [16, 17]: Interconnected network topology is adopted in HV transmission networks to provide a secure power supply in the event of an outage, as there are multiple paths to transmit electrical power. When you need to measure higher voltages, the PT reduces the measured voltage to that suitable for the voltmeter. In a static electric field, it corresponds to the work needed per unit of charge to move a test charge between the two points. “A” with two lines, one dotted and one solid, over it = DC current. The apparent power Since the voltage and current are always in phase, their product is always positive and, so power always flows from the source to the resistive load. Then the. The uncertainty in a measurement, A, is often denoted as (delta)A (read “delta A”), so the measurement result would be recorded as A ± (delta)A. Star - All elements need to be equal to phase voltage/1. Following are the applications in which open-delta system is used −. For a coffee shop a red leg delta would be the wrong transformer. You can connect any 2-wire 240v loads between any two phases, even across the open side of an open Delta. If the Transformer is a center-tapped delta secondary and the installer has bonded the center-tap (the X4 conductor on a step-down Transformer, or an H4 on a step-up Transformer), then the phase conductors on the end of the center-tapped winding will have half the voltage potential to ground of the line-to-line voltage, and the opposite. PT-Windings. The relationship between SOC and the discharging voltage at different currents can then be obtained, and the initial SOC during the discharging stage can be deduced. Figure 3. Connecting the probes without ground lead to the individual phases should be safe (though with limited common-mode rejection ratio), as long as you observe the overvoltage category rating of both the probes and the scope. Open delta or wye transformers; Low torque output causing mechanical stresses;. The intensity or brightness of the display is sometimes called the Z-axis. Written by Willy McAllister. # 5. The results can be seen in the following example: If each of the transformers are rated at 50 kVA and the secondary voltages are 240 volts, then the coil current of each transformer is 50,000/240 = 208 A. A residual voltage of 110 V is obtained in both cases. 071/22. The standard way to measure resistance is to pass a current through the resistor and measure its voltage drop (see Figure 1). Same as with two 9V batteries, it's 18V between ends, 9V over one battery and 0V center, and -9V between other battery and 0V center, and you are able to measure polarity because it's DC. thus increasing the voltage measurement across the ADC. 2. The star point forms a floating neutral. be identified Sat 17 Mar 2018 04. For the circuit shown above, the phase voltage is 120 volts. b) If the terminal PT is open-delta or wye-ungrounded (VT3 unavailable), the third-harmonic neutral undervoltage element (27TN), which uses VN3, is applied. LISNs are used to make conducted emissions measurements as well as provide a stable line impedance used to replicate power lines associated with the EUT/DUT. The equation is: I = Δ V R. 4 to 600V) on each primary. Having to deal with a single 35. 8 kV) connected Phase A to Phase B on one. 732I ph. Terminal 2 – SMU2: Set to Current Bias (VMU) with a test current of 0A. High power measurement requires highly accurate transformers to reduceThe secondary voltage Us is mostly: – 100 V or 110 V according to IEC for open-delta configuration. 32 kVA. in units of watts. on and measure the voltage across the rheostat. 56. The V-V connected transformers are used to supply a combination of large 1-phase and smaller 3. Typical Setting: 5% with 1 Sec TD 100 % Stator E/F ProtectionThis is how we can obtain the three different voltages for this system; however, we can also have a corner-tapped Delta configuration. 4 kV autotransformer. A = 18. By measuring the voltage across these two ends, we would be able to determine the temperature difference, (Delta T), between reference point and test environment. Figure 12 – Three-phase, three-wire, 2 wattmeter method. No. . 00E–06 1. It is as follows: Capacity of open delta system = √3 x rating of one transformer = √3 x 5 KVA= 8. 577 × Rating of the. Open-delta circuit should be grounded from only one point shown as Figure-1. The high-voltage (HV) test lead is placed on the H1 bushing terminal and the low-voltage (LV) test lead is placed on the H3 bushing terminal. Remember: "phase" means a coil or capacitor between two lines or between a line and a neutral. 00E–06 0. Did he bring in the correct 2 phases (i. The open delta voltage transformer reduces the AC voltage and large current proportionally to a value that can be directly measured by the meter ( automatic. PT-Name Plate. So from what I can tell, the following questions should be asked of the electrician: 1. Using a power quality analyzer connected to the drive input, first measure at the input side of the drive. The voltage to ground of any phase of the supply conductors accordingly is 277 V. The high-leg delta (also known as the wild-leg, stinger leg, bastard leg, high-leg, orange-leg, red-leg, and dog-leg delta) is a three-phase electrical service connection. These are the general setup and may vary and depend on the installation e. . Single Phase Voltage and Single Phase Current _____ 6 2B. Use A,B,N set A phase of the Omicron to 30 degrees and connect to A of the PT connection, Set B phase of the Omicron to 90 degrees and connect to C of the PT connection. open delta Configuration. Open delta is also used in industrial applications to form a delta-delta transformer connection when both the primary and secondary transformers have similar voltage ratings. This. They are commonly used in residential environments and have a power factor of 1. Low Reading. Delta Airlines is one of the leading airlines in the. This can be used to simplify resistance measurement. Typical coverage 95% Of Stator Winding. Silicon solar cells on high quality single crystalline material have open-circuit voltages of up to 764 mV under one sun and AM1. To properly size a delta/delta transformer, the transformer phases (windings) must be balanced. Schweitzer Engineering Laboratories, Inc. The existing ground on the center tap of the 120/240 Volt transformer will safely ground the delta. An open delta often has a grounded neutral connection on one of the transformers. With resistors, R 3 and R 4 reversed, the same current flows through the series combination and the voltage at point D, which is also the voltage drop across resistor, R 4 will be: V R4 = 0. edu. Fifty volts is considered safe for exposure to uninsulated conductors. Voltage transformer with two secondary windings, one Y-connected and one Open delta connected Figure 5. When looking at the raw data in the trigger trace function it shows single Va, Vb, and Vc phasors with L-L values. , artificial neural network. 4-wire open. 18. They feature four and eight measurement channels, respectively. On a Wye it reads 120 deg. Photo: TestGuy. 4: A voltmeter is placed in parallel with a resistor to measure the voltage across the resistor. The overvoltage relay is tuned to the third harmonic. I was not trying to answer any technical question, I was trying to answer an English one. For three-phase applications, two of these units are connected in open-delta (3P3W) and three units are required for wye-wye connections (3P4W). The system you are describing is called a 240/120V 3 phase 4 wire system. S. Under full (fault impedance is zero) earth fault situation in unearthed systems, the measured value from open-delta connection would be approximately 100V . The performance of. The test measurements I took were accurate enough, mostly within 0. An electric current is injected into the ground through two electrodes, and the voltage difference is measured between two other electrodes (Fig. Existing approaches include using downstream measurements to estimate tap positions of open-delta regulators [69] or using a voltage sensitivity-based approach to estimate excessive tap changes. Thus no multimeter can provide such a value directly, because measuring open circuit voltage is an abstract idea. Make 3 measurements -- AC, BC, and AB between nodes A&C, B&C and A&B. – 120 V according to IEEE for open-delta and star configuration. The basic design topology of the VFD with a diode bridge, DC bus capacitors and insulated gate bipolar transistor (IGBT) output has proven to be reliable and beneficial from application and financial perspectives. As long as all three "LINES" are connected, the phase between line 2 and line 1 is "seen" by the two lines. Divide this voltage by the resistance of the load to get the current. Conceptually, the delta measurement is far more accurate than the single measurement, because the delta measurement cancels the saturation current and all. Other voltages for open-delta connection can also be supplied based on customer requirement. (The total load carried by open delta system is 57. Not enough information. When one Line faults to ground, the primaries become open-delta configured with a voltage increase ratio of √3 (e. Measure and calculate the Open Delta voltage unbalance frequently and consider installing a VFD if the unbalance is more than 1 percent in the three-phase circuit. Open Delta Conection of Voltage Regulators. The wattmeter, ammeter and the voltage are connected to their primary winding. 5 Volts. In reply to #3. The voltage drops across all three resistors should add up to the supply voltage as defined by Kirchhoff’s Voltage Law (KVL). 3 shows a typical voltage transformer. In this case, both VT3 and the neutral third harmonic (VN3) measured across a neutral grounding transformer (NGT) are used. In essence one side of the secondary Delta is physically missing, however an electrical measurement is still possible across the missing side and so it is 3 phase. where 120 V is the nominal phase -to-phase secondary voltage: • V A – V N = 120∠30 (ABC), 120∠–30 (ACB) • V B – V N = 0 (ABC and ACB. Setting Values-V 0 - 6. The NI 9225 is rated for 600 V ch-ch isolation, so this voltage is within the safety specifications. 096v) and voltage divider. It involves two delta-connected transformers and. The Open-Delta SVR configuration has been well-known 1. You will notice that the power output. 4kV e. In-Band Voltage Excursions Synchrophasor Measurements Use IEEE C37. With respect to the A -phase current (I A) as reference (0 degrees) as shown in Figure 2, inject the following voltages into the relay, where 120 V is the nominal phase -to-phase secondary. A 20kΩ per volt voltmeter indicated a reading of 250 V on its 300 V scale when used to measure an unknown voltage. e. Snyder, PE PDH Online | PDH CenterThe open delta configuration is used for small motors, and the wye configuration is used for large machines. Either by calculation or by vector drawing. Dec 4, 2020. 86. It used this single L-N nomenclature except they are actually L-L. After determining which transformer is bad in a 3-phase bank, there are. The devices that have an internal 12-bit sigma delta Voltage ADC feature inputs with pre-scaling to enable sampling Li-Ion cell voltages directly, but also other. This is another method of closing the delta triangle. PT-Windings. With the power off and the primaries still wye connected, open the delta and reverse the connections for one of the secondaries, but leave the delta open. 577 x 15 KVA= 8. The maximum load power that can be supplied will a. #3.