Outage management

Conventional outage causes include natural ones such as weather and heat, excavations, power station defects, damage to power lines or other parts of the distribution system, a short circuit, the overloading of electricity mains, equipment failures, or cars hitting utility poles. The solution to effectively manage power outages lies in either implementing  outage management system (OMS) or upgrading an existing system.

An outage management system (OMS) is a utility network management software application used by operators of electric distribution systems to assist in restoration of power. OMS manages unscheduled and scheduled outages of distribution infrastructure like Distribution Transformers (DTs), HT/LT feeders etc. It collect information about outages from various systems and report the operator for taking corrective actions through crew management and remote control enabling customer satisfaction, improve System Availability and Reliability. Major functions usually found in an OMS include:

• Prediction of location of use or breaker that opened upon failure.
• Prioritizing restoration efforts and managing resources based upon criteria such as locations of emergency facilities, size of outages, and duration of outages.
• Providing information on extent of outages and number of customers impacted to management, media and regulators.
• Calculation of estimation of restoration times.
• Management of crews assisting in restoration.
• Calculation of crews required for restoration.

OMS Principles and Integration Requirements

At the core of a modern outage management system is a detailed network model of the distribution system. The utilities Geographic Information System (GIS) is usually the source of this network model. By combining the locations of outage calls from customers, a rules engine is used to predict the locations of outages. For instance, since the distribution system is primarily tree-like or radial in design, all calls in particular area downstream of a fuse could be inferred to be caused by a single fuse or circuit breaker upstream of the calls.

The outage calls are usually taken by call takers in a call center utilizing a customer information system (CIS). Another common way for outage calls to enter into the CIS (and thus the OMS) is by integration with an Interactive Voice Response (IVR) system. The CIS is also the source for all the customer records which are linked to the network model. Customers are typically linked to the transformer serving their residence or business. It is important that every customer be linked to a device in the model so that accurate statistics are derived on each outage.

More advanced Automatic Meter Reading (AMR) systems can provide outage detection capability and thus serve as virtual calls indicating customers who are without power. However, unique characteristics of AMR systems such as the additional system loading and the potential for false positives requires that additional rules and filter logic must be added to the OMS to support this integration.

Outage Management Systems are also commonly integrated with SCADA systems which can automatically report the operation of monitored circuit breakers. Another system that is commonly integrated with an outage management system is a mobile data system. This integration provides the ability for outage predictions to automatically be sent to crews in the field and for the crews
to be able to update the OMS with information such as estimated restoration times without requiring radio communication with the control center.

It is important that the outage management system electrical model be kept up to current so that it can accurately make outage predictions and also accurately keep track of which customers are out and which are restored. By using this model and by tracking which switches, breakers and fuses are open and which are closed, network tracing functions can be used to identify every customer who is out, when they were first out and when they were restored. Tracking this information is the key to accurately reporting outage statistics.

 

OMS Benefits

OMS Benefits include:

• Reduced outage durations due to faster restoration based upon outage location predictions.

• Reduced outage duration averages due to prioritizing

• Improved customer satisfaction due to increase awareness of outage restoration progress and providing  estimated restoration times.

• Improved media relations by providing accurate outage and restoration information.

• Fewer complaints to regulators due to ability to prioritize restoration of emergency facilities and  other critical              customers.

• Reduced outage frequency due to use of outage statistics for making targeted reliability improvements.

PST (Phase Shifting Transformers)

Phase Shifting Transformers (PST), able to control active power by regulating the voltage phase angle difference between two nodes of the system. The operation principle is voltage source injection into the line by a series connected transformer, which is fed by a tapped shunt transformer. So, overloading of lines can be eliminated. A typical phase shifting transformers may be capable of a variable phase angle shift up to 20°.

However, the speed of phase shifting transformers for changing the phase angle of the injected voltage via the taps is very slow. Phase shifting transformers and similar devices using mechanical taps can only be applied for very limited tasks with slow requirements under steady state system conditions.

Quadrature booster is a specialised form of transformer used to control the flow of real power on three-phase electricity transmission networks. For an alternating current transmission line, power flow through the line is proportional to the sine of the difference in the phase angle of the voltage between the transmitting end and the receiving end of the line. Where parallel circuits with different capacity exist between two points in a transmission grid (for example, an overhead line and an underground cable), direct manipulation of the phase angle allows control of the division of power flow between the paths, preventing overload. Quadrature boosters thus provide a means of relieving overloads on heavily laden circuits and re-routing power via more favourable paths. Alternately, where an interchange partner is intentionally causing significant “inadvertent energy” to flow through an unwilling interchange partner’s system, the unwilling partner may threaten to install a phase shifter to prevent such “inadvertent energy”, with the unwilling partner’s tactical objective being the improvement of his system’s stability at the expense of the other system’s stability. As power system reliability is really a regional or national strategic objective, the threat to install a phase shifter is usually sufficient to cause the other system to implement the required changes to his system to reduce or eliminate the “inadvertent energy”.

 

A phase shifting transformer typically consists of two separate transformers: a shunt unit and a series unit. The shunt unit has its windings connected across the phases. If it produces output voltages proportional to, and in phase with, the primary-side phase voltage then series transformer will produce a change in voltage magnitude. Alternatively, shunt transformer can be constructed so that its output voltages proportional to the primary-side phase-to-phase voltage. Since the line voltage between two phases in a three-phase system is always in quadrature with the voltage of third phase, the series transformer will introduce a small change in voltage magnitude but a large change in voltage angle.

 

The overall output voltage is hence the vector sum of the supply voltage and the phase shifted component. Tap connections on the shunt unit allow to control the output voltage and thus the power flow on the circuit containing the phase shifting transformer may be increased (boost tapping) or reduced (buck tapping) as shown in figure below.

 

Plug in Hybrid Electric Vehicles (PHEV)

A plug-in hybrid electric vehicle (PHEV), plug-in hybrid vehicle (PHV), or plug-in hybrid is a hybrid electric vehicle which utilizes rechargeable batteries, or another energy storage device, that can be restored to full charge by connecting a plug to an external electric power source (usually a normal electric wall socket). A PHEV shares the characteristics of both a conventional hybrid electric vehicle, having an electric motor and an internal combustion engine (ICE); and of an all-electric vehicle, having a plug to connect to the electrical grid.

The cost for electricity to power plug-in hybrids for all-electric operation has been estimated at less than one quarter of the cost of gasoline. Compared to conventional vehicles, PHEVs reduce air pollution locally and dependence on petroleum. PHEVs may reduce greenhouse gas emissions that contribute to global warming, compared with conventional vehicles. PHEVs also eliminate the problem of range anxiety associated with all-electric vehicles, because the combustion engine works as a backup when the batteries are depleted, giving PHEVs driving range comparable to other vehicles with gasoline tanks. Plug-in hybrids use no fossil fuel at the point of use during their all-electric range.

Greenhouse gas emissions attributable to operation of plug-in hybrids during their all-electric range depend on the type of power plant that is used to meet additional demand on the electrical grid at the time and place where the batteries are charged. If the batteries are charged directly from renewable sources of the electrical grid, then the greenhouse gas emissions are essentially zero. Other benefits include improved national energy security, fewer fill-ups at the filling station, the convenience of home recharging, opportunities to provide emergency backup power in the home, and vehicle-to-grid (V2G) applications.

Types of PHEV

Series hybrids use an internal combustion engine (ICE) to turn a generator, which in turn supplies current to an electric motor, which then rotates the vehicle’s drive wheels. A battery or supercapacitor pack, or a combination of the two, can be used to store excess charge. With an appropriate balance of components this type can operate over a substantial distance with its full range of power without engaging the ICE. As is the case for other architectures, series hybrids can operate without recharging as long as there is liquid fuel in the tank.

 

Parallel hybrids, such as Honda's Insight, Civic, and Accord hybrids, can simultaneously transmit power to their drive wheels from two distinct sources—for example, an internal combustion engine and a battery-powered electric drive. Although most parallel hybrids incorporate an electric motor between the vehicle's engine and transmission, a parallel hybrid can also use its engine to drive one of the vehicle's axles, while its electric motor drives the other axle and/or a generator used for recharging the batteries. This type is called a road-coupled hybrid. Parallel hybrids can be programmed to use the electric motor to substitute for the ICE at lower power demands as well as to substantially increase the power available to a smaller ICE, both of which substantially increase fuel economy compared to a simple ICE vehicle.

 

Series-parallel hybrids have the flexibility to operate in either series or parallel mode. Hybrid powertrains currently used by Ford, Lexus, Nissan, and Toyota, which some refer to as “series-parallel with power-split,” can operate in both series and parallel mode at the same time.