Common Technical and Application Questions about Distribution Transformers 1. What replacement parts available for transformers? Response: Other than enclosure parts, there are very few parts of is transformer that can be field-replaced. The various enclosure parts can be replaced in the field. There is a complete listing of these sheet steel parts on pages 9-113 and 9-114 of the Distribution Products & Services catalog. Enclosure parts are identified by frame number, not style number or kVA. Make sure you obtain the frame number off of the transformer nameplate prior to ordering any enclosure parts. 2. Can 60Hz transformers be used at other frequencies? Response: Transformers rated for 60 Hz can be applied to circuits with a higher frequency, as long as the nameplate voltages are not exceeded. The higher the frequency that you apply to a 60 Hz transformer, the less voltage regulation you will have. Although it is permissible to use 60 Hz rated transformers at higher frequencies, it is recommended that you do not apply lower frequencies to them…you should not use 60 Hz transformers in 50 Hz applications. 3. Can single-phase transformers be used on a three-phase source? Response: Yes, any single-phase transformer can be used on a three-phase source by connecting the primary terminals of the single-phase transformer to any two wires of a threephase system. It does not matter whether the three-phase source is three-phase 3-wire or three-phase 4-wire. The output of the transformer will be single-phase. 4. Can transformers be used to create three-phase power from a single-phase system? Response: No, transformers cannot be used to shift phases. Phase shifting devices (reactors or capacitors) or phase converters are required to change single-phase power to three-phase. 5. What considerations need to be taken in to account when operating transformers at high altitudes? Response: At altitudes greater than 3,300 feet (1,000 meters), the density of the air is lesser than at lower elevations. This reduces the ability of the air surrounding a transformer to cool it, so the temperature rise of the transformer is increased. Therefore, when a transformer is being installed at altitudes greater than 3,300 feet above sea level, it is necessary to de-rate the nameplate kVA by 0.3% for each 330 feet (100 meters) in excess of 3,300 feet. 6. What considerations need to be taken in to account when operating transformers where the ambient temperature is high? Response: Cutler-Hammer dry-type transformers are designed to operate in areas where the average maximum ambient temperature is 40°C. If you cannot wait for a custom-designed transformer to be manufactured to fit your application, and opt to use a standard unit, it is necessary to de-rate the nameplate kVA by 8% for each 10°C above 40°C.
7. What is the normal life expectancy of a transformer? Response: When a transformer is operated under ANSI/IEEE basic loading conditions, the normal life expectancy of a transformer is 20 years. The ANSI/IEEE basic loading conditions are: (a) the transformer is continuously loaded at rated kVA and rated voltages, (b) the average temperature of the ambient air during any 24-hour period is equal to 30°C and at no time exceeds 40°C, (c) the altitude where the transformer is installed does not exceed 3,300 feet (1,000 meters). 8. What are Insulation Classes? Response: Insulation classes were originally used to distinguish insulating materials operating at different temperatures. In the past, letters were used for the different designations. Recently, insulation system temperatures (°C) have replaced the letters designations. Previous Designation Class A Class B Class F Class H Class R
Insulation System Rating (°C) 105 150 180 220 220
9. How do you know if the enclosure temperature is too hot? Response: UL and CSA standards strictly regulate the highest temperature that an enclosure can reach. For ventilated transformers, the temperature of the enclosure should not increase by more than 50°C in a 40°C ambient at full rated current. For encapsulated transformers, the temperature of the enclosure should not increase by more than 65°C in a 25°C ambient at full rated current. This means that it is permissible for the temperature of the enclosure to reach 90°C (194°F). Although this temperature is very warm to the touch, it is within the allowed standards. A thermometer should be used to measure enclosure temperatures, not your hand. 10. Can transformers be reverse-connected (reverse-fed)? Response: Yes, with limitations. Cutler-Hammer single-phase transformers rated 3 kVA and larger can be reverse-connected without any loss of kVA capacity or any adverse affects. On transformers rated 2 kVA and below, there is a turns ratio compensation on the low voltage winding that adjusts voltage between no load and full load conditions. Three-phase transformers with either delta-delta or delta-wye configurations can also be reverse-connected for step-up operation. When reverse-feeding a delta-wye connected transformer, there are two important considerations to take in to account: (1) The neutral is not connected, only the three phase wires of the wye system are connected, (2) the ground strap between X0 and the enclosure must be removed. Due to high inrush currents that may
be created in these applications, it is recommended that you do not reverse-feed transformers rated more than 75 kVA. Cutler-Hammer manufacturers transformers designed specifically for step-up operation. 11. Can transformers be connected in parallel? Response: Yes, with certain restrictions. For single-phase transformers being connected in parallel, the voltages and impedances of the transformers must be equal (impedances must be within 7.5% of each other). For three-phase transformers, the same restrictions apply as for single-phase transformers, plus the phase shift of the transformers must be the same. For example, a delta-wye-connected transformer (30°-phase shift) must be connected in parallel with another delta-wye-connected transformer, not a delta-delta connected transformer (0° phase shift). 12. Why is the impedance of a transformer important? Response: The impedance of a transformer is important because it is used to determine the interrupting rating and trip rating of the circuit protection devices on the load or line side of the transformer. To calculate the maximum short circuit current on the load side of a transformer, use the following formula: Maximum Short Circuit Load Current (Amps)
=
Full Load Current (Amps) Transformer Impedance
Full load current for single-phase circuits is: Nameplate Volt-Amps Load (output) Voltage and for three-phase circuits the full load current is: Nameplate Volt-Amps Load (output) Volts X Square Root 3 (1.732)
Example: For a standard three-phase, 75 kVA transformer, rated 480 Volt delta primary and 208Y/120 Volt secondary (catalog number V48M28T75J) and impedance equal to 5.1%, the full load current is 75,000 VA 208V X 1.732
= 208.2 A
The maximum short circuit load current is 208.2 A = 4,082.4 A .051 The circuit breaker or fuse on the secondary side of this transformer would have to have a minimum interrupting capacity of 4,083 Amps at 208 Volts. A similar transformer with lower impedance would require a primary circuit breaker or fuse with a higher interrupting capacity. 13. What clearances are required around transformers when they are installed? Response: All dry-type transformers depend upon the circulation of air for cooling; therefore it is important that the flow of air around a transformer not be impeded. UL 1561 requires that there be no less than 6 inches clearance between any side of a transformer with ventilation openings and any wall or obstruction. In compliance with NEC 450-9, CutlerHammer ventilated transformers have a note on their nameplates requiring a minimum of 6 inches clearance from the ventilation openings and walls or other obstructions. This clearance only addresses the ventilation needs of the transformer. There may be additional local codes and standards that affect installation clearances. Transformers should not be mounted in such a manner that one unit will contribute to the additional heating of another unit, beyond allowable temperature limits…for example where two units are mounted on a wall one above the other. Additional technical information and application-related information is available on-line in C-H Expert.
LINE 38 Control and Encapsulated Transformers Tips Product Mini-power centers Single and three phase
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• • Type EP Buck Boost transformers Single phase
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Applications Industrial plants - anywhere there is 480 or 600 volt distribution & there are loads requiring 208 &/or 120 volts, e.g. workbenches, assembly lines, test equipment. Construction sites - temporary power, plant expansions, WWTP’s Commercial sites - car washes, parking lots, warehouses Industrial/Construction - small voltage change, e.g. need to run a 230 volt motor from 208 volt plant distribution system. Residential - outdoor low voltage lighting
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• Type EP General Purpose transformers Single phase
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• • Type EPT General Purpose transformers Three phase
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Industrial/Construction - Loads such as motors & lighting; bank 2 or 3 units to supply 3 phase loads; connect as autotransformers to serve 575 & 600 volt loads most economically. OEM - Large control power requirements on products such as chillers, power transformer fans. Commercial sites - Schools, hospitals, office buildings, restaurants, amusement parks, picnic shelters. Industrial/Construction - general distribution loads in applications where a NEMA 3R product is needed (e.g. outdoors, dusty atmosphere).
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Sales Hints NEMA 3R enclosure contains transformer, load center, primary & secondary main breakers and spaces for feeder breakers (as many or more than SQD, GE & Acme, the only competitors); saves up to 30% on installation time & cost. Available options: stainless steel cases, electrostatic shields, copper windings.
When connected as autotransformers, these give very economical solutions to voltage changes ranging from 5% to 20%. The buck boost slide rule simplifies the sizing, selection and wiring. Most distributors have several ratings in stock but frequently they aren’t ours. The styles with 12/24 secondaries are ideal for outdoor low voltage lighting; enclosures are NEMA 3R. NEMA 3R enclosures allow installation almost anywhere. See page 9-81 in 2003 Distribution Products Catalog (CA07101001E) for single and three phase autotransformer arrangements. Available options: stainless steel cases, electrostatic shields, copper windings, custom voltages, 50/60 HZ, Hazardous Location (Class I Division 2) Premium transformer with ratings that overlap the ventilated type DT-3 from 15-75 kVA Available options: stainless steel cases, electrostatic shields, copper windings, custom voltages, 50/60 HZ.
Product Types EPZ & EPTZ Class I Division 2 transformers – single & three phase
Application • Industrial – Hazardous locations such as in refineries, chemical plants, mills.
Type AP Control Power Transformers Single phase
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OEM - Control power requirements inside other electrical equipment such as MCC’s, low voltage switchgear.
Sales Hints • The interior of the case is completely filled with sand/resin encapsulation material and all leads are brought out through pipe elbows so that installer can make connections in an adjacent explosion proof junction box. Labeled as “Suitable for use in Class I, Division 2 Group C and D locations as defined by the NEC Article 501 with NEC recommended installation procedures for dry type transformers rated under 600 volts operation”. • Open type transformer with terminals on top of sand/resin encapsulation. Octagon shaped case fits tight spaces. Can be banked for 3 phase control power. • Available options: electrostatic shields, copper windings, custom voltages, 50/60 HZ
Product Industrial Control Transformers ypes MTE, MTK, MTA, MTC
Application • OEM - Control voltage supply for high inrush loads like starters, drives, in control panels, conveyor systems, pump panels, commercial sewing machines, machine tool equipment, commercial A/C, etc. • Industrial MRO - many equipment upgrades or modernizations necessitate larger control transformers.
Sales Hints • MTE is “state of the art” epoxy encapsulated design which is the standard in C-H MCC’s & enclosed control. Use SA-1239A for overview & the binder, B1228A for application details. W34 has a large stock of both fused and unfused designs as well as a complete family of CE certified units for export applications. • The MTG Universal type has a multitude of voltages for users who only want one style for all possible applications. The MTG has been successfully superceded by the MTE design – same Form, Fit and Function, with the epoxyencapsulated design! • The MTK is a 115° C design that is more economical for 750 to 5000 VA applications. • Almost all distributors (even “pure construction” houses) have some control transformers in stock. Often they are not ours because no one has asked for the business. Ask for the order! • There is a large installed base of equipment with Westinghouse type MTA and MTC. Replacements for these can be a lucrative business for our distributors.
Transformer Common Objections/Issues 1. Our in-to-stock prices aren’t competitive. Response: Cutler-Hammer understands the importance of maintaining competitive in-tostock price levels on transformers. If I can get a copy of the current “hot sheet” from the other competitor, I will forward that information to my pricing team and we’ll get your prices adjusted to meet the competitive price levels. Additional follow-up questioning needs to occur on this subject: In exchange for adjusting their DSP price levels, we need to get their commitment to stock a certain dollar amount or quantity of transformers. We also need to ask for the initial stock order! Cutler-Hammer is the only transformer manufacturer that sells transformers with freight prepaid and allowed for any quantity or dollar amount. All other manufacturers have a minimum invoice amount or minimum weight before they pay the cost of freight. Make sure you are comparing the total cost of any competitor’s transformers to our total cost when you are setting up pricing. Freight cost can add an additional 4% to 10% to the total cost of a transformer. 2. We’ve experienced freight damage on your transformers in the past. Have you addressed that issue? Response: Yes, we have addressed the major causes of freight damage on transformers. Our transformer plant has made extensive use of Lean Enterprise concepts to address this issue. We have implemented two programs that have resulted in significant reductions in freight damage; “lean shopping” and “lean shipping”. There is additional information on this subject in a PowerPoint presentation titled “DTDT Lean Shipping.ppt” 3. You can reach inside the ventilation opening of a transformer and touch the core-coil assembly. Is that normal? Response: Per UL, the enclosure of a transformer is designed to protect the internal parts of the transformer from accidental contact, not intentional contact. If a transformer is installed in a location that is readily accessible to people, instead of being installed in an electrical room, Cutler-Hammer does offer rodent screens as a field-installable accessory that may help to alleviate this concern. 4. Our primary competition includes an electrostatic shield as standard in their transformers and they don’t charge anything additional for it. The list prices of our shielded transformers are greater than the unshielded ones so our pricing is higher. Response: Cutler-Hammer, like the other major transformer manufacturers (Square D and General Electric) do not include an electrostatic shield as standard in their transformers. Most customers don’t care if the transformer is shielded or not. Why include the additional cost of the shield in 100% of the products you sell when less than 10% of the customers require it?
When this objection is brought up, you need to determine whether or not the customer really wants the shield. Many distributors simply cross the competitor’s catalog number to our catalog number, so if the competitor we are displacing includes a shield in 100% of their product, the cross-reference will result in a shielded transformer. For those customers who do actually care and require a shielded transformer as standard, we will meet the competitor’s price level and sell them shielded transformers for the same unit price as our standard unshielded product. Your pricing manager can assist you in setting up the proper pricing. 5. Our transformers say that they are “Made in Mexico” on them. My customers want (or require) products that are “Made in the USA”. Response: It is true that our transformer manufacturing plant is located just across the border from El Paso. Many “American” transformer manufacturers are relocating their manufacturing facilities to Mexico. Square D, GE, Acme, Hammond, and Federal Pacific are examples that come to mind. Our manufacturing facility is a modern, state-of-the-art facility that is ISO9002 and ISO14001 certified. We also utilize 6-Sigma and Lean Enterprise. Although the actual manufacturing and assembly is performed in Mexico, the majority of materials used to build our transformers are purchased from companies located in the U.S. and the raw materials used to make the components are American components. If documentation is required to show what percentage of a specific transformer is U.S. content, that information can be provided. Also, Cutler-Hammer manufactured transformers meet all of the requirements of NAFTA. In the unusual circumstance that a customer insist the transformer state “Made in USA” on the nameplate, we can provide those as a special item. 6. There doesn’t appear to be enough room inside your transformers to make the necessary electrical connections. Response: All of our transformers meet or exceed the wire bending requirements set forth by the National Electric Code. Cutler-Hammer’s ventilated transformers, as a family, have the smallest footprint of any manufacturer. One of the trade-offs that goes along with a small footprint is the width and depth of the bending space may be smaller when compared to a competitor’s product.
