UPS power accessories –the Isolation Transformer Cubicles and PDU’s.…
The Basic functions of these Isolation Transformers are as below:
· Providing electrical Isolation with Secondary neutral (common) grounding to a dedicated earth.
· If galvanically shielded it provides electrostatic isolation and common mode noise rejection for Surges and Spices.
· It also provides harmonic mitigation of triplens due to Delta Zigzag or Delta Star configuration.
· When a pair of Isolation Transformer with different vector group such as 3Phs Delta Star and 3Ph Delta - Delta at the input of dual redundant parallel UPS system, the 30 degree phase Shift of both the transformers provides mitigation of 5th and 7th harmonics.
· They provide capacity to handle and deliver non-linear loads containing spectrum of harmonics without over heating or burning.
· After lot of research the problem and causes of failures of conventional transformers on non linear harmonic loads, was analysed to be excessive heating of them and not being suitable for such loads. UL & ANSI organization then came up with a derating curve as guideline for use of conventional transformerson on non linear type load .These became guideline under UL 1564 & ANSI 57.110.
· This section provides a curve which specifies % derating for use of normal transformers on non linear harmonic loads for different K factors.
· They also specified methods and formula for calculating the K factors of a complex harmonics non-linear load systems worked on the basis of % harmonic for individual harmonics.
Datsons sensed this niche requirement 7-8 years ago and after doing relent less effort in research and development by in depth study of the problem and making trials in designs and structural arrangement on various prototypes , came up with a range of capacities from 30 Kva to 600 Kva of K-7, K13, and K20 rated transformers and validated their performance with testing for oversized loading covering harmonic stray losses which was the single most important critical factor in addition to Skin effect of conductors and eddy current losses.
The PDU with built in K rated Isolation Transformers which today is key equipment in Data Center installations including intelligent monitoring with microprocessor based metering and Branch Circuit monitoring and communication ports such as RS-485 for remote monitoring of various parameters and status of various protection switchgears was the next development at Datsons.
DATSONS has successfully delivered thousands of systems with K-rated transformers in 3 PH having capacity spread from 30 KVA to over 1000 KVA and are working on prestigious installations all over India for last number of years.
For more about DATSONS click on About us.
The fundamental frequency Stray field and stray losses get multiplied by K factor for harmonics currents.
DATSONS K rated transformer have winding geometries optimized for lowest stray losses
· Minimising the stray field and stay losses is the most critical challenge of nay k rated transformer design.
For more details on K rated transformers please see special note on the same.
Started as a Technocrat family Concern , more than two decades ago,it began with manufacture of 3 Ph Induction motor protection devices , followed by voltage stabilisers for domestic appliances.
In the early 90’s the UPS systems used to be double conversion type with built in magnetics such as rectifier and inverter Transformers and mostly had low voltage battery bus. Later with the advent of high voltage IGBTs the DC bus voltages rose from low of 48 V to 300+ V DC etc. The designs used 6/12 pulse rectifiers using SCR’s and later IGBTs directly to covert mains AC voltages into DC voltages without stepping down by the rectifier and inverter transformers.
This reduced the size – weight as well as cost of the UPS and internal power dissipation of the rectifier transformers.
Yet the output inverter isolation transformer continued for a while.
Progressively the UPS designs changed to transformer-less
systems with IGBT inverters which used PWM high frequency switching technology requiring very low filteration of the high
frequency switching modulation yet with double conversion – AC- DC-AC.
The systems now were totally free of magnetics excepting very small ferrite chokes in the output.
The modern UPS’s became lighter compact and less in heat generation.
But this led to one major limitation, as there was no electrical isolation between the mains and the floating output with no common wire at zero potential.
The modern UPS having all its output wires floating, none could be grounded as common /neutral for use with the load.
Any computer installation requires an AC supply which has its common wire at ground potential.
The magnetic-less UPS designs had their output floating with respect to ground (both wires being live (Hot) could not be grounded as required for a computer supply.
Here came the need for an external isolation transformer that could provide zero potential common wire by grounding one of the wires in isolated secondary to a dedicated earth.
The computer power supply being a rectifier – capacitor input type power supply having a non linear harmonic loads with high content of 3 rd , 5 th ,-------,11 th etc. harmonics. Therefore the isolation transformer had to be double wound type having 1:1 ratio but suitable for handling non linear harmonic loads.
This led to a special class of transformers called as K rated Transformers by UL and ANSI.
A few years later Datsons indigenously developed Power Conditioners –a combination of Shielded Isolation Transformers and Servo - Controlled Voltage Stabilisers for Industrial CNC machines and got market acceptance for almost all the Domestic as well as international brands of CNC machine manufacturers along with electro-medical diagnostic systems and high tech laboratory applications.
A hot standby source to UPS.
During mid 90’s , medium power UPS installations
created a new niche requirement - a regulated and isolated AC bypass power source as a hot redundant bypass source in parallel with the UPS connected through Static Bypass Switch. These UPS were having configurations such as - 3 Ph input – 3 ph output and 3 Ph input -1 Ph output both and hence the bypass source also needed similar configurations such - a combination of an open Delta VEE configuration Isolation Transformer which converted 3 ph power to 1 ph source and a 1 ph AC Servo Controlled Voltage Stabiliser. DATSONS catered to such requirements of almost all Domestic and multinational UPS – OEMS.
Power Conditioners for CNC machines and other apps :