Cover Story | August 2016
Discoms should be penalised for low PQ
Man Mohan Rathi | Vice President (Power Plant), Shree Cement Ltd
What are the measures that may be taken to improve the power supply scenario?
The following measures may be taken to improve overall Grid Power Supply Scenario:
a) Installation of FACTS - Flexible AC Transmission System devices as mentioned earlier
b) Uniform code of conduct for power transmission and distribution of each state
c) Implication of legal penalty rules for distribution companies (discoms) as applicable for utilities (Today discoms impose penalty on utilities for low PF, over and under drawl. Similar penalties can be imposed on discoms for low power quality supply and unplanned power cuts)
d) Improvement of protection system to avoid cascade tripping following total system failure.
e) Increase in system reliability measures to be rewarded for the motivation of discoms.
f) Implementation of regular hot line maintenance practices and regular transmission/distribution lines to identify any obstacle (like trees) which lead line tripping. As per our knowledge these practices have been implemented by reputed private organisations and central government organisations (i.e. PGCIL). But it is lacking in state level transmission/distribution systems.
How do you think the power supply scenario compares with advanced countries?
There are some improvements in the past 5 years. But looking at present and future industrial growth, India is far behind in power quality and reliability in comparison to advanced countries due to:
a) Lack of common code of conduct for all discoms.
b) High local interference in transmission and distribution system (Theft of Power, Damage to Power lines, Theft of equipment)
c) No concrete philosophy for providing Quality of Power to consumer, every measure is taken at consumer end only.
d) Implementation of ring main system to replace radial system for better system reliability.
What are the power quality (PQ) issues you face in your day-to-day operations and how do you handle them (Including through internal team or a service provider)?
We face two types of PQ issues in our day to day operations:
a) From Service Provider : Voltage Profile Base - We face load level bus voltage unbalance followed by Grid input voltage unbalance resulting in heavy current disturbance and motor/equipment overheating, which increase the chances of failure. To control grid voltage disturbance at HT level there are options available like IGBT controlled auto reactive power controller (i.e. STATCOM - Static Compensator, UPFC - Unified Power Flow Control, SSSC - Static Synchronous Series Compensator for AC system). All these controllers are costly affairs.
b) From Internal Source : Harmonic Profile Base - There are 6 pulse LT VFD utilised in the system, resulting in heavy 5th & 7th harmonic level which may lead to overheating of equipment (Source transformer, Motor and Cable), increase system losses, and sometimes malfunctioning of equipment.
We can come out from this issue by using higher pulse VFD (i.e. 12 Pulse - Limitation in design for below 75 kW), by use of chocks & active filters (slightly increase heat losses), by use of K factor transformer or oversized transformer to cater to additional thermal load due to harmonics, by optimum combination of sources (To avoid high harmonic level by increasing load on source - switch off low load source & transfer it to another source)
What are the power quality equipment you use to monitor and mitigate the problems and please narrate their uses?
We use two types of power quality equipment to measure and record power quality. a) Mobile Power Analyser like Krykard ALM35. To measure all electrical related parameters like Voltage, Current, Power - Active / Apparent / Reactive, Power Factor (PF) including individual (up to 63rd harmonic level) and total harmonic level.
b) Fix type of energy meter installed at every major incoming & outgoing feeders - This will help monitor real time total Harmonic Level (THDV - Voltage & THDC - Current) and help decide corrective actions to mitigate the same
In an ideal situation what kind of QoP supplies do you expect from the discoms and what are the inadequacies you are facing now?
In an ideal situation we expect balance supply voltage (< 1 per cent unbalance) at every level with smooth sine wave supply (THDV < 3 per cent and THDC < 5 per cent as per IEEE 519).
We are facing unbalance voltage supply problems with frequent sag and swells in voltage amplitude.
- BS Srinivasalu Reddy