Showing posts with label power plant operation. Show all posts
Showing posts with label power plant operation. Show all posts

Saturday 6 June 2015

8 Major Advantages of Distribution Automation



8 Major Advantages of Distribution Automation
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Economic Challenges
More and more electric utilities are looking to distribution automation as an answer to the three main economic challenges facing the industry:
  1. The rising cost of adding generating capacity,
  2. Increased saturation of existing distribution networks and
  3. Greater sensitivity to customer service.[/info_box]
Therefore, utilities that employ distribution automation expect both cost and service benefits.
These benefits accumulate in areas that are related to investments, interruptions and customer service, as well as in areas related to operational cost savings, as given below:

1. Reduced line loss
The distribution substation is the electrical hub for the distribution network.
A close coordination between the substation equipment, distribution feeders and associated equipment is necessary to increase system reliability. Volt/VAR control is addressed through expert algorithms which monitors and controls substation voltage devices in coordination with down-line voltage devices to reduce line loss and increase line throughout.

2. Power quality
Mitigation equipment is essential to maintain power quality over distribution feeders.
The substation RTU in conjunction with power monitoring equipment on the feeders monitors, detects, and corrects power-related problems before they occur, providing a greater level of customer satisfaction.

3. Deferred capital expenses
A preventive maintenance algorithm may be integrated into the system. The resulting ability to schedule maintenance, reduces labour costs, optimizes equipment use and extends equipment life.

4. Energy cost reduction
Real-time monitoring of power usage throughout the distribution feeder provides data allowing the end user to track his energy consumption patterns, allocate usage and assign accountability to first line supervisors and daily operating personnel to reduce overall costs.

5. Optimal energy use
Real-time control, as part of a fully-integrated, automated power management system, provides the ability to perform calculations to reduce demand charges.
It also offers a load-shedding / preservation algorithm to optimize utility and multiple power sources, integrating cost of power into the algorithm.

6. Economic benefits
Investment related benefits of distribution automation came from a more effective use of the system. Utilities are able to operate closer to the edge to the physical limits of their systems. Distribution automation makes this possible by providing increased availability of better data for planning, engineering and maintenance.
Investment related benefits can be achieved by deferring addition of generation capacity, releasing transmission capacity and deferring the addition, replacement of distribution substation equipment. Features such as voltage/VAR control, data monitoring and logging and load management contribute to capital deferred benefits.
Distribution automation can provide a balance of both quantitative and qualitative benefits in the areas of interruption and customer service by automatically locating feeder faults, decreasing the time required to restore service to unfaulted feeder sections, and reducing costs associated with customer complaints.

7. Improved reliability
On the qualitative side, improved reliability adds perceived value for customer and reduce the number of complaints. Distribution automation features that provide interruption and customer service related benefits include load shedding and other automatic control functions.
Lower operating costs are another major benefits of distribution automation.
Operating cost reduction are achieved through improved voltage profiles, controlled VAR flow, repairs and maintenance savings, generation fuel savings from reduced substation transformer load losses, reduced feeder primary and distribution transformer losses, load management and reduced spinning reserve requirements.
In addition, data acquisition and processing and remote metering functions play a large role in reducing operating costs and should be considered an integral part of any distribution automation system. Through real time operation, the control computer can locate the faults much faster and control the switches and reclosures to quickly reroute power and minimize the total time-out, thus increasing the system reliability.

8. Compatibility
Distribution automation spans many functional and product areas including computer systems, application software, RTUs, communication systems and metering products. No single vendor provides all the pieces. Therefore, in order to be able to supply a utility with a complete and integrated system, it is important for the supplier to have alliances and agreements with other vendors.
An effective distribution automation system combines complementary function and capabilities and require an architecture that is flexible or “opens” so that it can accommodate products from different vendors.
In addition, a distribution automation system often requires interfaces with existing system in order to allow migration and integration, still monitoring network security.
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Thursday 21 May 2015

Important Guidelines to Startup and Shutdown a Large Generator Operating Conditions

The purpose of these guidelines is to ensure the continuing operational integrity of generators.


Operating conditions (startup and shutdown) that have forced units off-line or have damaged or shortened the life of turbine (or generator) components in the past are highlighted in the guideline to prevent recurrences in the future.

Startup Operation
Shutdown Operation

Startup Operation

In addition to monitoring the various generator support systems for cooling and lubrication, electrical

Parameters, temperatures, and vibration, inattention to the following areas has caused problems in the past:

Problem #1

At no time should excitation interlocks or protective relay functions be bypassed or disabled for the purpose of energizing a generator’s direct current (DC) field winding.

Problem #2

For generators requiring field pre-warming, the manufacturer instructions and established procedures should be followed relative to the allowable field currents.

Problem #3

A generator field should not be applied or maintained at turbine speeds above or below that recommended by the manufacturer. On cross-compound units where a field is applied at low speeds or while on turning gear, extreme caution must be exercised.

Should either or both shafts come to a stop, the field current should immediately be removed to prevent overheating damage to the collector or slip rings.

Problem #4

After the field breaker is closed, the generator field indications should be closely monitored. If a rapid abnormal increase occurs in field current, terminal voltage, or both, immediately open the field breaker and inspect the related equipment for proper working condition before reestablishing a field.

Problem #5

During off-line conditions, at no time should the field current be greater than 105% of that normally required to obtain rated terminal voltage at rated speed in an unloaded condition.

Typically, turbo-generators are designed to withstand a full load field with no load on the machine for only 12 seconds; after that, severe damage can occur to the stator core iron laminations.

Problem #6

When synchronizing a generator to the system, the synchroscope should be rotating less than one revolution every 20 seconds Phase angle differences should be minimized and no more than 5 degrees out of phase when the circuit breaker contacts close.

Phase angle differences as little as 12 degrees can develop shaft torques as high as 150% of full load and damage shaft couplings and other turbine and generator components. Manufacturers usually recommend limiting maximum phase angle differences to 10 degrees. 

It is also desirable that incoming and running voltages are matched as closely as possible to minimize reactive power flow to or from the electrical system.

In general, the voltages should be matched within 2% at the time of synchronization. The speed of the turbine should be slightly greater than synchronous speed prior to breaker closure to help ensure that the unit will not be in a motoring condition following connection to the electrical system, and the generator voltage should be slightly higher to ensure VAR flow into the system instead of into the generator.

NOTE: Under no circumstances should operators allow a unit to be synchronized using the sync-check relay as the breaker-closing device (i e , holding a circuit breaker control switch in the closed position and allowing the sync-check relay to close the breaker). Some sync-check relays can fail in a “closed” state, allowing the circuit breaker to be closed at any time.

Shutdown Operation

Normally, units are removed from service through operator initiation of distributed control system (DCS)

Commands or turbine trip buttons that shut down the prime mover. Closure of steam or fuel valves will then initiate anti-motoring or reverse power control circuits that isolate the unit electrically by opening the generator circuit breakers, field breakers, and, depending on the design, unit auxiliary transformer (UAT) low side breakers. If limit switch circuitry or anti-motoring/reverse power relays fail to operate properly, the unit may stay electrically connected to the system in a motoring condition. 

If excitation is maintained, this condition is not harmful to the generator. However, the turbine blades may overheat from windage. On steam units, the low pressure turbine blades are impacted the most, with typical withstands of 10 minutes before damage.

However, the unit can be safely removed from service with the following operating steps:

Operating step #1

Verify that there is no steam flow or fuel flow in the case of combustion turbine units to ensure that the unit will not over speed when the generator circuit breaker(s) are opened. 

Operating step #2 

Transfer the unit auxiliary power to the alternate source if opening the unit breakers will de-energize the UAT.

Operating step #3

Reduce or adjust the generator’s output voltage (voltage regulator) until the field current is at the no load value, and transfer from automatic voltage regulator mode to the manual mode of operation.

Operating step #4

Open the generator circuit breaker(s). 

Operating step #5

Open the generator field breaker
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