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Harmonics is an insidious enemy that the current day electrical distribution systems are being bombarded with. Spread by non-linear loads, such as variable frequency drives (VFDs), rectifiers, LED lighting and UPS, harmonic currents and voltages corrupt the sinusoidal nature of the power supply. Whilst the impact of this on transformers is well known (excessive heating and losses), the impact on downstream Medium Voltage (MV) and Low Voltage (LV) switchgear is equally catastrophic. Harmonic suppression does not just deal with the quality of power but is a critical method of dealing with the very essence of your electrical system the switchgear that controls and isolates power.
The Hidden Stress on Switchgear Components
Switch gear is also set to operate at a specific frequency and voltage typically 50 or 60 Hz. Harmonics result in high-frequency currents that wreak havoc on the mechanical and thermal integrity of switchgear components. Harmonic currents have the potential to affect the tripping of the thermal-magnetic devices in circuit breakers. The Eddy current causes additional heating of conductive parts, busbars and connections induced at harmonic frequencies. This raises the aging rate of insulation and the resistance of mechanical joints. The skin effect may create current flow along conductors surfaces at higher frequencies effectively reducing the ampacity of conductors and resulting in hotspots. Ryan Transformer system design considers the total harmonic distortion (THD) so that the switchgear and transformers may operate as a unit and not be subjected to unexpected failures that cause costly down time.
How Transformers Become the First Line of Defense
Transformers will always provide some impedance to harmonics, and special designs are required to effectively reduce them. In this case the distinction between a conventional distribution transformer and a harmonic-reducing (or K-rated) transformer comes about. Normal transformers are not concerned with the eddy current loss that result due to non-linear loads; they overheat and run out of life early.
We can tailor our transformers and particularly VPI line (and even our drytype cast resin models) at Ryan Electric to incorporate harmonic suppressive characteristics. We reduce the transmission of zero sequence harmonics (including the 3th harmonic) between LV side and MV side with the aid of electromagnetic shielding and core designs. This prevents harmonic currents flowing into an upstream that creates stress to the MV switchgear. In addition, our transformers, by design, offer a buffer when connected in a unit substation, which concentrates the harmonic distortion on the load side and does not subject the primary switchgear to an unnecessary electrical load.
Phase Shifting: The Key to Cancellation in Rectifier Applications
In large rectifier systems (e.g. electrolysis, metal refining or large data centers) the most desirable form of harmonic suppression is achieved before the harmonics ever reach the switchgear. Phase-shifting transformers are accomplished in this way.
Ryan Electric specializes in multi-pulse-rectifier (12-pulse, 24-pulse, and 48-pulse) transformers. They are really the predecessors of the rectifiers, which causes a phase shift between the second windings, so that the harmonics produced by the rectifiers (the 5th, the 7th, etc.) can cancel out in the transformer proper. The amount of current flowing around the primary side, and through the MV switchgear, is much cleaner. This passive harmonic suppression lowers the level of RMS current passing through switchgear busbars and breakers, lowers operating temperatures and extends the life of these essential components, with no high-cost active filters.
System Integration and Compliance with Global Standards
Harmonic suppression requires a system view of the electrical system. There exists no transformer in a vacuum; it must be joined with switchgear and measuring and protection relays to form a robust network. The solutions provided by Ryan Electric consider this integration. Our mini substation transformers and unit substations provide an interim to the MV supply and distribution to LV.
We ensure that our equipment is of high international standards including IEEE 519 that requires the maximum level of harmonic distortion that may be present at the common coupling point. Our manufacture and testing of our transformers and matching switchgear ideas allows the entire system and not just the transformer to be protected. To ensure that when our equipment is installed in the field it does effectively protect MV and LV switchgear against the devastating effects of harmonic distortion, we test performance at simulated harmonic loads at our CNAS approved test laboratories and assure reliability to our customers at Microsoft data centers and to national utilities.
Expert Transformer Solutions
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