#2. Snyder, PE PDH Online | PDH CenterThe open delta configuration is used for small motors, and the wye configuration is used for large machines. The star-delta starter has both advantages and disadvantages. If you can shut things down see what voltages look like with no load. 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. 1a). 2 kV/26. Up until the last 10 years open delta was the common 3 phase configuration in these parts. The open delta system provides a total of 75% of the basic rating of the full system. 0V OPTION 1 NOTE: FILTER, FERRITE BEAD are optional OPTION 2 SN6501 (Transformer Driver) 5V_CNTL GND GND_ISO TLV70450 (5. 58. 173 kVA Select from the following choices Choose the correct. plus or minus 0. The simple explanation is under nominal conditions (NC) we have a wye-delta configuration and open the delta at one corner to measure the summed voltage of zero under nominal conditions. The voltage you measure will often vary with the loading of the system (on a perfectly balanced 240V delta you might measure 138V to ground). As a temporary measure, when one. 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. So to display the units or multiples of units for either Resistance, Current or Voltage we would use as an example: 1kV = 1 kilo-volt – which is equal to 1,000 Volts. 100 KVA d. 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. Most voltmeters are self contained and come with scales ranging from 150V to 750V. PT-Windings. 86. It’s employed when a three phase transformer needs to supply both single and three-phase power (or transformer bank). Operation Criteria for relay-Figure-5. 3V) bases. 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. Open delta. Advantages. Other types of three-phase supplies are wye connections, ungrounded delta connections, or corner-grounded delta ("ghost" leg configuration) connections. - Measurement at the open delta winding: Here, the displacement voltage is determined directly by the measurement. 65,740/1,000=65. 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. cn). Step 2. neutral wire may be needed for three phase 240V outlets etc. Because chromel and alumel are different materials and have different Seebeck coefficients, the voltage at the two reference points are also different. I G D D S V DS +-V BV DSS is determined when I D reaches 250μA. A three-point-delta method provides more accurate resistance measurements in low-voltage applications. The wye configuration gives a better voltage balance than the open delta configuration. 7% of the capacity of a complete Δ-Δ circuit of the same transformers. 2. The supply voltage of the transformer is 480/277 V. 1 in. 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. Then, place the two leads of the meter on either side of the load. Responding to Anonymous' query: (1) The 'high-leg' 3-phase system is more properly referred to as a center-tapped (high-leg or red-leg) 4-wire, delta system. The building in question has only a single phase meter center. on and measure the voltage across the rheostat. In this work the self-discharge characteristics are evaluated through resting OCV (open-circuit voltage)-SOC (state-of-charge) hysteresis and storage aging behavior for pouch NCM|graphite lithium-ion battery. Reduced starting current by 33% of what the direct online starting consumes, meaning it is economical in terms of electricity consumption. You can do that with a two-step. Set the appropriate compliance voltage, and check the Measure Voltage box (VB). g. 6%, i. +-Open Access Article This Open Access Article is licensed under a Creative Commons Attribution-Non Commercial 3. I might add that normally these 3 transformers would be built as one chunk of steel with 3 sections, one for each phase. 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. Delta and wye networks are used in conjunction with three-phase power (as you will see below, the delta configuration is also found in a bridge rectifier circuit). ; 1mA = 1 milli-amp – which is equal to one thousandths (1/1000) of an Ampere. on and measure the voltage across the rheostat. The terms line current and phase current follows the same logic: the former referring to the current through any one line conductor, and the latter to the current. That is why a 3-phase motor can be connected to a delta, open delta, Y (or 'star', or 'Pi') system,. For a coffee shop a red leg delta would be the wrong transformer. It can only come from a true three phase utility service. Typical coverage 95% Of Stator Winding. The open delta voltage transformer configuration consists of two (2) double bushing VTs connected as shown in Figure 1. Exercise 9-3 - The Open-Delta Connection; 30329 - AC/DC Motors and Generators Open manual. Delta Star is mostly used at Medium Voltage level e. ]. Where I is current, Δ V is electric potential difference, and R is resistance. 2n. They feature four and eight measurement channels, respectively. 1 ± 0. Because the unit for current is ampères, or amps, the symbol for it is A. 2) Because this is 3-phase the difference in phases is 120 degrees. Figure 7 – Delta connection – three phase, three wires. e. Most VTs are designed for 60 Hz but can also be designed for other frequencies. e. Three-phase power is linked in a delta configuration. Figure 1. 3 V is used so that the maximum solid ground relay voltage would be 3 × 69. Similarly, the next phase is between line 1 and line 3. All three line-to-line voltages are calculated using three-wire, open delta voltage measurements from the generator and bus PT inputs. Connected to a numeric. 3 in. To overcome this difficulty two seperate limbs are provided in the magnetic circuit of three phase voltage Transformer to form Five limb Voltage Transformer as shown in fig. Balance the loads on the transformer windings as follows: 3-phase loads: one-third of the load on each of the phases. Open Delta is a 3 phase transformer bank using 2 transformers. edu. In the open Delta, the voltages are 120-240 single phase and 240V three phase. The excitation current may be increased to get 25% more than the rated voltage. Voltage Dividers Circuit. Connect voltage inputs that are wye-connected, open-delta-connected, or single voltage. This parameter will be used to sweep the dc value of the voltage at input node A. e. Voltage transformers are devices that allow the measurement of voltage in electrical circuits included in the power system. 6 Residually connected voltage transformers The three voltages of a balanced system summate to zero, but this is not so when the system is subject to a single-phase earth fault. The correct voltage reading is _____. 1) This is a typical delta to wye configuration. It does notify the potential energy stored as electrical charge in an electrical supply point. We have two existing PT's connected in open delta (connected line to line (A with B) and (C with B)) to a. The resulting electric current is measured in coulombs (C) The SI unit of measure for the number of electrons that pass a given point in 1 second; it is defined as 6. 73 times greater than, True and more. Voltage transformers with two secondary windings, one for connection in Y and the other in broken delta can then. 16. A common three-phase source connection scheme is the Delta high-leg or Four-wire Delta, where each phase coil outputs 240 volts: Identify the different voltages obtained from this coil configuration, and which connection points each voltage is. prior to this observation unit had. The voltage you measure will often vary with the loading of the system (on a perfectly balanced 240V delta you might measure 138V to ground). 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. Electronic components are continuing to shrink as consumers demand faster. 73. Silicon solar cells on high quality single crystalline material have open-circuit voltages of up to 764 mV under one sun and AM1. Gate pin is shorted to Source pin. 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). Search for:. The V-V connected transformers are used to supply a combination of large 1-phase and smaller 3. A vector amplitude calculation. delivered to the drive. 0 V olts. Chaniotakis and Cory 11 +-R1 R2 R3 R4 Vs AB. For example, if each transformer has a rating of 100kVA, then the kVA rating of the open delta. The maximum load power that can be supplied will a. A typical example is shown in Figure 3 below. I asked them to take voltage readings between phase-phase and phase-ground just to make sure it is an un-grounded delta secondary. rsd =0 L1 L2 L3 Open delta winding for ground fault. - May 16, 2021. They feature four and eight measurement channels, respectively. The open-delta PT is commonly used in medium-voltage (MV) generator paralleling switchgear among other applications. A. Connect N to B phase. 1 above). First, the low-voltage 50-V class isn't really a "class" as such but rather a safety rating. 11/05/2014 1:07 AM. An open delta system is a three-phase power system in which one phase of the power circuit is not connected. Per north American standards the primary side leads the secondary low voltage side by 30 0. 7% of the capacity of a complete Δ-Δ circuit of the same transformers. 5% at 20VA. However, a slightly more compli-cated approach is required when dealing with open-delta PTs. e. Finally, there are different ways of measuring three-phase. 2. The voltage generated in the secondary terminal of a current transformer can be defined as: V S = (R L x I S). 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. This technical article describes the basic principles of three-phase systems and the difference between the different measurement. When measuring winding resistance, the reading should be observed and recorded once the resistance value has stabilized. 118 synchrophasors, and is the economical solution for overcurrent protection. Use line a as the common potential point. measurement, current/voltage measure-ment and mA-outputs. Make sure that the single-phase loads are balanced on the Center-Tapped Delta and that unbalance in the three-phase connection is 1 percent or less. 30 10ps 10ps 100ns 2. For nominal low voltage applications, the motor protection relay shall be able to internally measure a voltage up to 600 VAC 50/60 Hz per UL standards or 690 VAC, 50/60 Hz per IEC. Feel like buying Chris a coffee? Think of it as SchulerRuler fueler! transformers in this guide are de-signed to transform primary voltages from 5 – 34. It does this by reducing the effects of any small errors present in the winding of either the primary or secondary coils of the transformer. PT-Name Plate Specifications. 732V L I L =. 1. # 5. High-precision battery cyclers can maintain constant currents with very little variation and can measure and store voltage and current with very little measurement. and voltage measurement. Most people are accustomed to the single. When you have a triangle of 3 resistors (a, b, c), and nodes A, B, C. In star connection, the phase to neutral voltage is about 58 % of the phase to phase or line voltage. of the VT, only A and C phase measurements are in-phase. A differential input is balanced because the gains and. When connecting three transformers for three-phase use with a delta secondary, a voltage test should be done before closing the secondary. If the loading question 7 is connected in wye, what would be the line voltage and the line current supply in the load? 104. subsequent Voltage ADC measurements. 68. 7% of closed delta system) You can better understand the above calculation with the circuit diagram given in. Vectorally the three phases total zero deg. Let, Vph – Phase Voltage of each secondary Iph – Phase current of each secondary In a closed delta connection, the line voltage is equal to the phase voltage. SIRIUS XHS LV: Highly isolated low voltage analog input. The star point forms a floating neutral. In this other system, we typically take the B Phase and ground it, so when we measure A-C, C-B, or B-A, the result is 240V; A and C to ground will yield a measurement of 240V, as well, but B to ground. Voltage imbalance is the measure of the voltage differences between the phases of a three-phase system. Phase and negative-sequence voltage and current are shown. Voltage across open (missing transformer) was pretty off maybe 10--15%. V A = 3 V L I p h And for the open delta connection: V A = 3 V L I p h Taking the ratio of open delta to closed delta power, gives: 3 V L I p h 3 V L I p h = 0. 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. You can connect any 2-wire 240v loads between any two phases, even across the open side of an open Delta. To make the transformer connections compatible with three-phase supplies we need to connect them together in a particular way to form a. Also, recall that phase difference between Line current and Line-Line voltage (phase to phase voltage) is 30°. A residual voltage of 110 V is obtained in both cases. Re: Difference Between Closed Delta and Open Delta Arrangement of Elements. U. Open-Delta Step Voltage Regulator (SVR). No neutral comming in. Aug 11, 2014. The most basic method of taking voltage measurements is to count the number of divisions a waveform spans on the oscilloscope’s vertical scale. On balanced situations, there is no current flow at open- delta circuit. This solution eliminates the need for the CT which. 707. Agilent measure-ment instruments, such as network analyzers, LCR meters, and impedance analyzers range in frequency up to 325 GHz. The Open-delta connection system is usually only used in emergency conditions, as its efficiency is low when compared to the delta-delta (Closed delta) system. In this application, an open delta PT connection is used to detect zero-sequence voltage at the generator terminals. 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. If either side of the PT were wired in a delta, it would cause a 30° voltage phase shift and incorrect readings. 1 General requirements on equipment 37 A 3. Figure 2. Specifically in delta. Resistor a is connected between nodes B & C; resistor b between A & C, and c between A & B. Compared to a grounded-wye arrangement the open-delta PT only requires two. A transformer can not act as a phase changing device and change single-phase into three-phase or three-phase into single phase. Instrument voltage transformers can also be referred to potential transformers (PTs). slavag (Electrical) 6 May 08. A. 577 (or 57 . Image used courtesy of Amna Ahmad. Open delta- two xformrs, not broken. Testing Instrument with accompanying ATPOL 8. Usually, star – delta overvoltage relay is used to prevent a failure, supplied by open-delta voltage transformers. If the system is utilizing wye-connected PTs, the voltages measured are in phase with the individual phase voltages. 1. Having to deal with a single 35. In the case of VTs with two secondary windings (one secondary winding for measurement, and one residual voltage secondary winding also known as a tertiary winding), it is advisable to connect a resistance to the terminals of the open delta connected tertiary windings of the three transformers (see figure 2 below). -They can be used at substation where only open-delta Voltage Transformers (VTs) are available-Negative-sequence Directional Overcurrent were not widely used with traditional relays. 4. In a Delta Connection, we get only a single. Divide this voltage by the resistance of the load to get the current. The capacitors are connected in series at the primary side of the auxiliary transformer. Voltage Regulators basically is autotransformers that regulate the voltage in medium voltage power lines by boosting or bucking the voltage. Following are the applications in which open-delta system is used −. 3. This shift can be detected by measuring the Voltage across Grounding Resistor Or from the generator terminal Open Delta voltage. 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. The LibreTexts libraries are Powered by NICE CXone Expert and are supported by the Department of Education Open Textbook Pilot Project, the UC Davis Office of the Provost, the UC Davis Library, the California State University. Figure 4. Ratioed currents and delta voltage measurements are all made inside the part, and a voltage result is presented at the output, with a sensitivity of 4mV/°C. 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. High-voltage batteries for automotive systems are defined as those with ≥ 60 V. Current Transformer Winding Resistance Test Connections. isolated from all phases (and until tied down earth) any voltage. Figure 4. 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. A DMM gives you not an open circuit reading, but a reading across a 10Mohm resistor (typically). The open delta. 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. In medium voltage networks, the basic source of zero-sequence voltage measurements is the open delta system of classic voltage transformers (VTs). To properly size a delta/delta transformer, the transformer phases (windings) must be balanced. measurements of its input impedance, one when terminated in a short and another when terminated in an open, can be. I have a project where the existing pad mounted utility transformer is configured as delta-delta. 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. With all the three transformers connected in delta, the power delivered to the resistive load is. In the open Delta, the voltages are 120-240 single phase and 240V three phase. Looking at a 120/208 wye system, the phase voltage would be 120V and the phase-to-phase voltage would be 208V. In the substation, three single-phase transformers are connected in star- star Configuration and supplied three-phase power to consumers. So the sum of the voltage drops is: V T = 6 V + 12 V + 18 V = 36. 732 * Vp , where Vp is the line-to-neutral voltage. If the primary phase voltage in a typical delta/wye system is 480V, the secondary phase voltage is 120V. Not sure if that's the technical name or not. In any case, if SolarEdge inverter connected to a string of power optimizers, the string voltage will not exceed the maximum voltage specified in the inverter datasheet. Residual Voltage & Open Delta Voltage Measurement. ; 47kΩ = 47 kilo-ohms – which is equal to 47 thousand Ohms. The capacitive potential divider is used to divide the high line voltage to reduce it below 10kV. I have a delta delta transformer , 480 volts primary 230 volts secondary has worked fine until yesterday , have very low voltage on one phase of secondary , 230 volts a phase 230 volts b phase , and about 15 volts on c phase . Feel like buying Chris a coffee?. If it still measures approximately zero, adjust the rheostat to minimum resistance and measure the 3 secondary line-to-line delta voltages. In this case, both VT3 and the neutral third harmonic (VN3) measured across a neutral grounding transformer (NGT) are used. The open delta connection uses two single-phase transformers. 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. If either side of the PT were wired in a delta, it would cause a 30° voltage phase shift and incorrect readings. We know the phase-to-phase voltage is 4,160V. 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. You can connect any 2-wire 240v loads between any two phases, even across the open side of an open Delta. The measurement is similar to IEC 60270, yet the quasi-integration is conducted at a narrow bandwidth of 9 kHz with a tunable center frequency between 10 kHz to 10 MHz. 577 × Rating of the. 33/11kV as well at distribution voltage level of 11/0. 8 kV) connected Phase A to Phase B on one. 25×10 18 e − /s and relates electron potential (in volts) to energy (in joules): 1 J/1 V = 1 C. The scale is then proportioned to read the actual higher voltage being measured. The FET consists of 3 terminals, a source (S), drain (D), and gate (G). 3. thus increasing the voltage measurement across the ADC. Many motors (and some transformer windings) are connected in either a Delta (Δ) configuration (Figure 2, left) or in a Wye (Y) configuration (Figure 2, right). PT-Open Delta Connection. Under full (fault impedance is zero) earth fault situation in unearthed systems, the measured value from open-delta connection would be approximately 100V . zero volts. L2 L1 L3 Fault condition L2 L1 L3 Healthy condition L1 L2 L3 U. . The observed frequencies are subdivided into various groups: alpha (8–13 Hz), beta (13–30 Hz), delta (0. User manuals, specification sheets, CAD drawings and more. This. Also, one or both of the ungrounded phases may indicate low power factor because this type of. Below is a diagram of the open delta connection used in medium voltage measuring circuits. 5 Volts. Three-phase machinery typically runs from Delta voltage, a configuration using three hot wires and no neutral wire. and one for the open delta voltage signal. We can insert these definitions into the equation for power: power = d U d t = d U d q ⋅ d q d t = v i. Broken delta provides 3V0 only. Where: V L is the line-to-line voltage, and V P is the phase-to-neutral voltage. delta. A V-V connected transformer can be connected in parallel to delta-delta connected transformer but not to ___________ a) delta-star b) star-delta c) star-V d) all of the mentioned 2. 2. Delta wiring forms an equilateral. 577 x rating of closed delta system=0. Open delta provides phase-phase voltage only. In Digital Phosphor Oscilloscopes (DPO), the Z-axis can be. A phase angle meter connected A-phase to B-phase on a Delta source reads 60 deg for voltage. To select which signal each cursor is measuring, use the drop down box next to C1 and C2. The equation is: I = Δ V R. They are commonly used in residential environments and have a power factor of 1. Wye and Delta comparison. 09/01/2012. tinfoil (Electrical) 16 Jan 06 14:30. Understanding Power amp Power Quality Measurements. PDHonline Course E431 (2 PDH) The Square Root of Three (√3) in Electrical Calculations 2020 Instructor: David A. Voltage transformer with two secondary windings, one Y-connected and one Open delta connected Figure 5. 3-phase 4-wire system line-to-line voltage measurements are often a vector calculation of the line-to-neutral voltage measurements. A weak peak is found on the OCV-SOC curve of incremental capacity and differential voltage analysis. Question 10. The open delta configuration provides a simple means of voltage control, especially when more than one starting voltage is required. on and measure the voltage across the rheostat. I asked them to take voltage readings between phase-phase and phase-ground just to make sure it is an un-grounded delta secondary. Continuing in the three-phase realm, we discuss exactly how easy delta voltages are to figure out. The standard way to measure resistance is to pass a current through the resistor and measure its voltage drop (see Figure 1). The residual voltage of a system is measured by connecting the secondary windings of a VT in ‘broken delta’ as shown in Figure 4. If Neutral to ground voltage is low at the receptacle than system is healthy, If It. 3 phase using two transformers. 73 as there will be two elements across each phase. Sigma-delta (Σ-Δ) ADCs offer multiple benefits when designing RTD systems. The measurements were conducted in argon-purged 0. The components to set up the circuit are cheaply available relative to VFDs. Then we would say the length of the paper is 11. The floating Vn wire is just to show that the primary is delta only, neutral is not used. on and measure the voltage across the rheostat. A broken delta is used to measure 3Vo (the sum of the delta voltages) for a ground relay. The wattmeter, ammeter and the voltage are connected to their primary winding. Rated frequency 50 Hz; 60 Hz. Basic three-phase power. The word "open" can get confusing for some people at times when dealing in electrical. vehicle (HEV) or electric vehicle (EV), high-voltage batteries are used as storage elements to power the wheels. Good Answers: 225. Like the LTC2997, the LTC2990 and LTC2991 make all necessary measurement and temperature calculations internally. #1 I have been working with a power meter recently that has the voltage inputs from an "Open Delta" 3-wire PT arrangement. The Wye Connection – Phasor Addition. In this configuration, the PT primaries and secondaries are both wired in wye configurations. The maximum HT cutoff values for individual CD instruments differ, but they correspond to the maximum. It is the combination of capacitive potential divider & electromagnetic transformer (auxiliary transformer). The voltage terminals of the wattmeters are connected phase to phase. )A four-wire delta (4WD) electrical service is a three-phase delta service with a center-tap on one of the transformer windings to create a neutral for single-phase loads. 32 kVA. U. 346. The high leg is a nominal 208V to ground. Voltage between three Phases = 240V (3-Φ). Open Delta with 50KVA center tapped secondary 30ft away and 10KVA 3 spans away, secondary probably only #4. That makes the the L-L voltage the same as the L-G voltage for that system. 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. a power leg can only be found if the x2 of one of the transformers in the bank is grounded, & the power leg will. Averaging voltage measurements (from SMU2 and SMU3) taken at both a positive and negative test current will correct for voltage offsets in the circuit. Open Delta Conection of Voltage Regulators. Exercise 2 - Three-Phase Power Measurement; Exercise 3 - Phase Sequence; 86364 - Three-Phase Rotating MachinesOpen-circuit voltage is then a measure of the amount of recombination in the device. 5–4 Hz), and theta. mA = Milliamps. Re: How to measure 3phase 480VAC with oscilloscope. 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. WHY IS A VLF HIPOT USED INSTEAD OF A REGULAR 60 HZ. The polarity does not matter. Free Download Here pdfsdocuments2 com. open delta Configuration. Voltage imbalance is the measure of the voltage differences between the phases of a three-phase system. Single-Phase Generators – for smaller single-phase loads, these gensets usually do not go above 40 kW. 3. Variable frequency drives (VFDs) have been commonly used in industrial and commercial applications for decades. 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 Osilloscope's Graph. 577. Figure B2. In the case of a delta connection,. Study with Quizlet and memorize flashcards containing terms like equal to the voltage from line to line, 1. The intensity or brightness of the display is sometimes called the Z-axis. This is a measure of the voltage applied to the detector to amplify the small circular dichroism signal. We are Having a 300 MW generator for which the Secondary open delta voltage of 3rd set of PT's is gradually increasing, and the B phase PT is getting blown out, tapping for the 1st and the 2nd set of PT's derived from the same point as that of the 3rd one, secondary voltages of 1st and 2nd PT's are healthy. /2 2. Single- phase loads are connected to one leg of the wye between line and neutral.