India’s power distribution companies Discoms are responsible for the supply and distribution of energy to a variety of consumers (industrial, commercial, agriculture, domestic, etc.). This is also, according to the Brooking Institute, the weakest link in the power ecosystem from both a financial and operational sustainability perspective.
The quality of power quality
Of course, the provision of power is not just a matter of connecting households to the wires and collecting revenue for services rendered. It requires the provision of a consistently good quality of power to those consumers. This is especially true for industrial and commercial concerns operating within a Discom’s service area.
Voltage spikes, harmonics or interruptions – regardless of the duration – can and will damage equipment. In addition to the damage to sensitive equipment and subsequent costly repairs, power quality issues result in lost time, corrupt data, lower productivity and reduce the life expectancy of the equipment.
The Asian Power Quality Initiative highlights the importance of continuous power quality (PQ) monitoring, a move away from the more traditional ‘reactionary’ approach taken previously.
They state that “continuous monitoring of PQ is probably the only way ahead to accurately monitor and analyse the issues arising due to poor PQ.”
The resultant benefits include:
Proactive management: Enables trends to be identified and the risks to be extrapolated to safety and reliability within specific points in the electrical network.
Aids preventative and predictive maintenance: The insights into how the equipment reacts to specific PQ events or disturbances provides the foresight for taking timely remedial actions. It also allows the maintenance teams to optimise the preventive maintenance window by providing previously unavailable insights. Specific procedures to avoid interruptions and prevent failures can be designed based on data from continual monitoring.
With diagnostic capabilities for specific conditions, PQ monitoring can create a significant impact on the development of preventive maintenance programmes. Early detection of problems: PQ parameters specified to the network enable the system to identify and send alerts when conditions begin to deteriorate. This ensures the timely solution of PQ issues before they can cause damage.
Accurate planning for capital investment to improve PQ: A significant consideration is the ability to plan accurately for future capital investments due to real-time and historical data availability. Continual power quality monitoring provides access to this detailed information.
Ensuring compliance: The compliance and regulatory checklist for PQ parameters are continually expanding. PQ is an integral part of several internal quality control programmes, industry-specific norms and international standards.
Power Quality Data Interchange Format
One of the key goals of PQ monitoring is to be able to establish a benchmark for PQ, whether it’s across a facility or at an industry level. Continuous PQ monitoring is becoming increasingly adopted across the sector, accompanied by a rise in the diversity of PQ software applications, underlying database platforms, and logics to run simulations and analyse data.
A Power Quality Data Interchange Platform (PQDIF) specifies a common format for PQ measurement. The IEEE Power Engineering Society Task Force is standardising the data interchange format. The guidance provided by the neutral platform is key to ensuring a consistent form of data exchange between software and monitoring devices for its universal applicability.
Consumer-centric service contracts
SAIFI, SAIDI, MAIFI – while all are used to measure distribution system reliability, they may not be detailed enough to provide information about the reliability for two utilities with different feeders. Nor do they necessarily take into account the proportion of interruptions caused due to faults at the customer end.
Continuous PQ monitoring systems, however, provide more accurate insights which can be easily tracked and analysed to improve performance and get flexible contracts that reward customers maintaining good PQ.
Poor PQ is one of the root causes of business problems including productivity losses, downtime, loss of reputation and goodwill, customer dissatisfaction and much more.
Continuous Power Quality monitoring provides an opportunity to gain real-time insight into the health of a power system and is a vital and integrated part of the power system to maintain its reliability.
Smart Energy International spoke with Chintamani Chitnis, Head: Grid Operations, Power System Control Centre (PSCC) in Mumbai, about specific challenges being experienced within the state of Maharashtra concerning power quality.
Power Quality is an issue that has been taken very seriously by the transmission and distribution system operators in the state.
The distribution level network is almost 95% underground and is therefore little affected by extreme weather events. However, the transmission system is affected, and for this reason, automation of the system has been undertaken – through SCADA on the transmission side, and a distribution management system (DMS) on the distribution side – in order to minimise the impact on customers.
All operations at 220kV level are 100% automated, and all transmission networks are N -1 compliant, meaning that redundancy to the level of 100% is achieved in terms of consumers.
The subsequent System Average Interruption Frequency Index (SAIFI), System Average Interruption Duration Index (SAIDI) and Consumer Average Interruption Frequency Index (CAIFI) scores are the best in India and are comparable with the best in the world, says Chitnis. This is primarily due to the network planning being done in such a way as to enable continued connection to customers even if a feeder should be lost. Even if a feeder should be taken off the grid, there is always another feeder available.
Related in the distribution network the underground network automation systems are handled in such a way that the network is fully equipped with fault passage indicators and the ring main units are fully automated; thus many distribution substations have an auto-transfer scheme and manual intervention is totally avoided. Self-healing grid functionality is wholly decentralised, and there is no manual intervention at all from central control.
End-consumer interruptions thus sit at about 20 minutes a year. By utilising an ‘islanding system’, power supply in Mumbai is assured uninterrupted within the city limits. Disruptions to the grid in the Western Regional Power grid results in automatic isolation of the city from the rest of the grid.
The total customer base in Mumbai is about 3.5 million, with Chitnis’s team being responsible for 750,000 customers. The total consumer base is divided between four different utilities in Mumbai and consumers have the option to switch ‘wires’ to another utility as they wish.
“Unlike in other parts of the world where this likely happens only on the supply side, in Mumbai you can change even the wires,” says Chitnis.
“Therefore the continuity of supply you afford to the consumers is of paramount importance for each of the utilities. As a result, consumers switch for multiple reasons, including tariff or power quality.”
Automation on the transmission and distribution networks.
The distribution networks in the area are automated up to about 40% for big substations. Substations are automated in a ring configuration connecting two substations and smaller substations in-between.
“If there are ten substations in a ring, 50% of them will be automated. The philosophy of automation is provided in the first leg of the ring and somewhere in the middle – more commonly known as the mid-way operating point. In the case of a fault on either of the sides, you can switch the consumers to an alternate feeder. This is done with the help of fault passage indicators which are communicable and visible on the DMS. If an operator notices any tripping on the DMS, he automatically also sees what kind of fault passage indications are available on each of the stations and, based on the fault passage indicators, he isolates the section indicated and inferred to be faulty, and restores it.
The total restoration time we usually have in terms of automated substations is less than 2-3 minutes for each of these rings.
“At some critical consumer locations, we have an autochanger scheme where the operator doesn’t have to intervene, and there is an automatic change over to another supply in the event of the normal supply tripping, without any manual intervention. So within a matter of milliseconds this changeover happens.
“The communication is enabled through GPRS and fibre for the bigger substations. All of these assets are mapped on our GIS, and therefore in real-time we can see what areas are out of supply and restore the consumers who are affected.
The GIS is connected to the CRM, and this allows customer service representatives the opportunity to identify and provide accurate information on restoration efforts when they are speaking to customers who have called in regarding an outage.
On the transmission lines, the high rated substations are primarily gas-insulated substations and are 100% automated.
In addition to operations, transformers and voltage correction can be controlled remotely in cases where voltages fluctuations are experienced. There are various other alarms built in, where for instance, voltage variations are clearly highlighted. Overhead lines are equipped with auto reclosers which, in the event of a transient fault, will island the feeder and enable restoration of the line within a matter of milliseconds.
Cascading blackouts have been almost completely eliminated, but as a backup, load trimming is possible to reduce the load on a specific line and ensures the line remains active. This infrastructure means system load is controllable to avoid blackouts.
Disaster management plans are in place and the responsibility of the IT department.
However, IT and OT systems are kept entirely separate from one another, and it is through this that threats to the external network are minimised. Additional security features include compliance with international cybersecurity standards.
The fibre networks operate on a similar ring system to the topology, followed by the transmission and distribution networks.
And while the cellular networks do suffer command failures from time to time, the percentage of these are around 5% and considered fairly minimal. 95% – 97% is the norm in terms of communication availability across the network.
Longer-term outages which cannot be addressed by rerouting the supply, and which are caused by accidents on the physical grid, are dealt with swiftly.
Standard procedure is to provide portable generation to the affected areas, thereby restoring power supply. In most cases, supply is fixed and restored within a period of three hours. These kinds of incidents are rare, occurring perhaps once or twice per annum.
However, more of a concern to the utilities in Mumbai is the quality of the power on the network. Surges or dips in supply are primarily due to the interconnected nature of the grid and disturbances on the grid are carried down to consumer level – normally large industrial or commercial concerns – and manifest as voltage dips. These transient dips can impact machinery onpremise and result in significant cost for the consumer to repair.
Power quality considerations are controlled from two sides. On the one hand, it is from the load side, and the other is at a grid level.
The percentage of dips seen by consumers is directly proportional to the fault level of the system.
“As a system operator, and in consultation with the other transmission utilities and the state load and dispatch centre, we are trying to migrate from a continuous operation philosophy to a sectionalised operation philosophy. By sectionalising operations, it is anticipated that fault levels will go down drastically.
“What we have been able to do is reduce the magnitude of the voltage dips and thus voltage dips which previously were at 75% or 100% will now come down drastically to between 0%-25%. This means if 100kv is the voltage, you will now see a drop up to 75kv compared to previously when drops to 25kv were experienced.”
By sectionalising EHV buses and reducing fault levels by about 50%, the magnitude of the dips of the voltage has come down drastically, and therefore the consumer is almost immune to the voltage dips.
Because the duration of the voltage dip is also of importance and mostly a function of protection systems not operating correctly, any trip at the level of 220kV has to clear within 160 milliseconds.
What has been done to address this specific requirement is the installation of protection systems which have all numerical relays and are able to clear the fault within 160-200 milliseconds while also limiting the voltage dip to about 20%. All the equipment down the line is able to sustain this magnitude and duration dip.
Chitnis concludes: “This is how we have been able to mitigate the risk. We started this programme last year, and we are able to see that consumers remain unaffected for about 75% of the normal voltage dips that happen in the system.”
Chintamani Chitnis is the Head: Grid Operations at the Power System Control Centre (PSCC) in Mumbai.
Chitnis is also a confirmed speaker at India Utility Week, and you can find more information on his presentation and the event at www.india-utilityweek. com