In order to support proper decision making and O&M activities, DMS solution shall have to support the following functions:
- Network visualization & support tools
- Applications for Analytical & Remedial Action
- Utility Planning Tools
- System Protection Schemes
The various sub functions of the same, carried out by the DMS are listed below:
1) Network Connectivity Analysis (NCA)
Distribution network usually covers over a large area and catering power to different customers at different voltage levels. So locating required sources and loads on a larger GIS/Operator interface is often very difficult. Panning & zooming provided with normal SCADA system GUI does not cover the exact operational requirement. Network connectivity analysis is an operator specific functionality which helps the operator to identify or locate the preferred network or component very easily.NCA does the required analyses and provides display of the feed point of various network loads. Based on the the status of all the switching devices such as circuit breaker (CB), Ring Main Unit(RMU) and/or isolators that affect the topology of the network modeled, the prevailing network topology is determined.The NCA further assists the operator to know operating state of the distribution network indicating radial mode, loops and parallels in the network.
(2) State Estimation(SE)
The state estimator is an integral part of the overall monitoring and control systems for transmission networks. It is mainly aimed at providing a reliable estimate of the system voltages. This information from the state estimator flows to control centers and database servers across the network. The variables of interest are indicative of parameters like margins to operating limits, health of equipment and required operator action. State estimators allow the calculation of these variables of interest with high confidence despite the facts that the measurements may be corrupted by noise, or could be missing or inaccurate. Even though we may not be able to directly observe the state, it can be inferred from a scan of measurements which are assumed to be synchronized. The algorithms need to allow for the fact that presence of noise might skew the measurements. In a typical power system, the State is quasi-static. The time constants are sufficiently fast so that system dynamics decay away quickly (with respect to measurement frequency). The system appears to be progressing through a sequence of static states that are driven by various parameters like changes in load profile. The inputs of the state estimator can be given to various applications like Load Flow Analysis, Contingency Analysis, and other applications.
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(3) Load Flow Applications (LFA)
Load flow study is an important tool involving numerical analysis applied to a power system. The load flow study usually uses simplified notations like a single-line diagram and focuses on various forms of AC power rather than voltage and current. It analyzes the power systems in normal steady-state operation. The goal of a power flow study is to obtain complete voltage angle and magnitude information for each bus in a power system for specified load and generator real power and voltage conditions. Once this information is known, real and reactive power flow on each branch as well as generator reactive power output can be analytically determined.
Due to the nonlinear nature of this problem, numerical methods are employed to obtain a solution that is within an acceptable tolerance.The load model needs to automatically calculate loads to match telemetered or forecasted feeder currents. It utilises customer type, load profiles and other information to properly distribute the load to each individual distribution transformer. Load-flow or Power flow studies are important for planning future expansion of power systems as well as in determining the best operation of existing systems.
(4) Volt/ VAR Control (VVC)
Volt/VAR Control or VVC refers to the process of managing voltage levels and reactive power (VAR) throughout the power distribution systems. There could be loads that contain reactive components like capacitors and inductors (such as electric motors) that put additional strain on the grid. This is because the reactive portion of these loads causes them to draw more current than an otherwise comparable resistive load would draw. The erratic current results in both over-voltage/under-voltage violations as well as heating up of equipments like transformers, conductors, etc which might even need resizing to carry the total current. A power system needs to control it by scheming the production, absorption and flow of reactive power at all levels in the system.
A VVC application shall help the operator to mitigate such conditions by suggesting required action plans. The plan will give the required tap position and capacitor switching to ensure the voltage to its limit and thus optimize Volt Var control function for the utility.
(5) Load Shed Application(LSA)
Power system by its characteristics have long stretches of transmission line and multiple injection points, hence instabilities which lead to critical failure or un predicted system conditions are un avoidable. The instabilities usually arise from power system oscillations generated due to faults, peak deficit or protection failures. Distribution load shedding & restoration schemes plays a vital role in emergency operation & control in any utility. It detects the emergency situation and performs a predefined sets of control actions, like opening, closing of non critical feeders, reconfigure the downstream or sources of injections, or performs a tap control at transformer. Usually distribution network is complex and covers larger area, the emergency actions taken at downstream reduces lots of burden on upstream network. In a non-automated system, system awareness and operators ability to respond to the situation plays key role in mitigation. If the decisions are not fast enough, the problem can grow exponentially and causes major catastrophic failure.
DMS needs to provide a modular automated load shedding & restoration application which automates emergency operation & control requirements for any utility. The application should cover various activities like Under Frequency Load Shedding (UFLS), limit violation and time of day based load shedding schemes which are usually performed by the operator.
(6) Fault Management & System Restoration (FMSR)
Reliability and quality of power supply are key parameters which need to be ensured by any utility. Reduced outage time duration to customer, shall improve over all utility reliability indices hence FMSR or automated switching applications plays an important role. The two main features required by a FMSR are: Switching management & Suggested switching plan
The DMS application receives faults information from the SCADA system and processes the same for identification of faults and on running switching management application; the results are converted to action plans by the applications. The action plan includes switching ON/OFF the automatic load break switches / RMUs/Sectionalizer .The action plan can be verified in study mode provided by the functionality .The switching management can be manual/automatic based on the configuration.
(7) Load Balancing via Feeder Reconfiguration (LBFR)
Load balancing via feeder reconfiguration is an essential application for utilities where they have multiple feeders feeding a load congested area. To balance the loads on a network, the operator re-roots the loads to other parts of the network. A Feeder Load Management (FLM) is necessary to allow you to manage energy delivery in the electric distribution system and identify problem areas. A Feeder Load Management monitors the vital signs of the distribution system and identifies areas of concern so that the distribution operator is forewarned and can efficiently focus attention where it is most needed. It allows for more rapid correction of existing problems and enables possibilities for problem avoidance, leading to both improved reliability and energy delivery performance.
On a similar note, Feeder Reconfiguration is also used for loss minimization. Due to several network and operational constraints utility network may be operated to its maximum capability without knowing its consequences of losses occurring. The overall energy losses and revenue losses due to these operations shall be minimized for effective operation. The DMS application utilizes switching management application for this, the losses minimization problem is solved by the optimal power flow algorithm and switching plans are created similar to above function
(8) Distribution Load Forecasting
Distribution Load Forecasting (DLF) provides a structured interface for creating, managing and analyzing load forecasts. It should be designed to facilitate both “top-down” and “bottom-up” forecasting methodologies in the same environment without placing any restrictions on the types of models available and should support short-term, medium-term, as well as, long-term forecasting.
DLF provides data aggregation and forecasting capabilities that is configured to address today’s requirements and adapt to address future requirements and should have the capability to produce repeatable and accurate forecasts.
