Issue 01 / April 2010
Generator Sizing Pitfalls: How to Avoid Costly Mistakes
“Generator Sizing Pitfalls,” a program in Generac’s Professional Development Seminar Series, focuses on identifying and avoiding typical generator sizing mistakes. When it comes to generator sizing, the discussion can focus on sizing an entire facility or on a specific type of concentrated load. The majority of this training module focuses on the particulars of specific types of problematic loads:
- Motors
- Soft starters
- Variable frequency drives
- Various non-linear loads
- Uninterruptible power supplies (UPS)
Gensets are composed of an engine and alternator. The engine is the source of the power and determines the genset’s frequency response while the alternator is the power converter and determines the system’s voltage response. When an electric motor load is started, a significant transient occurs on the generator system. The effects of motors and various motor starting methods are discussed within this module with the goal of providing a deeper understanding, rules of thumb and help in avoiding potential problems.
The genset’s alternator is a relatively clean power source, but when applied to loads with high harmonic content, the alternator’s voltage may become significantly compromised with harmonic voltage distortion. Controlling harmonic voltage distortion levels while operating on the generator is critical to proper generator sizing. If the voltage distortion is too great, the loads may have problems operating correctly. To avoid this issue, various rules of thumb are discussed and the importance of utilizing sizing tools that perform harmonic analysis is explored.
When it comes to UPS sizing, everyone has an opinion about some magic multiplier for generator/UPS compatibility; but there isn’t one multiplier that works everywhere. The secret to UPS sizing is some basic understanding and probing questions:
- What are the UPS topology/type and input tolerances?
- What are the UPS harmonic levels? Are they filtered or not?
- Is the HVAC system backed up with the generator?
- What are the power factor rating and charge rates?
Typically, engineers rely heavily on manufacturer generator sizing programs, but too often these programs don’t incorporate the necessary input data for many of today’s more difficult loads. Generally, the problems with correct sizing and generator application involves limiting the generator’s transients (voltage and frequency dips) and load-induced harmonic voltage distortion to levels that are acceptable to the loads.
For more information on Generac’s Professional Development Seminar Series, please contact National Power. Generac also offers the newest/best sizing software in the industry called, Power Design Pro. You can find out more about the software at Generac.com/PowerDesignPro.
Greening World of Standby Power: Generac Complies with New EPA Regulations
In January 2008, the U.S. Environmental Protection Agency (EPA) released a final New Source Performance Standard (NSPS) for stationary spark-ignited engines, which provides for manufacturers to certify that an engine meets the emission requirements. To control emissions, units above 80 kilowatts (kW) require an active air-fuel ratio control combined with an exhaust catalyst, much like an automobile.
Generac was the first manufacturer to work with the South Coast Air Quality Management District (SCAQMD) to extend the Certified Emissions Program (CEP) to natural gas and propane units. Now, all Generac spark-ignited stationary gensets with power outputs from 25 kW to 300 kW are compliant with the new EPA regulations. These changes make Generac the leading provider of green natural gas/spark ignited/diesel gensets on the market.
Traditionally, standby power generation received emission exemptions for most of North America due to the product’s very limited run-time. The new EPA requirements will generally meet local air quality requirements, but markets with significant air quality issues may impose additional requirements beyond the national EPA requirements. Additionally, EPA emissions regulation now requires compliance by the end-user. For products uncertified by the manufacturer, engines must be subjected to an on-site testing and certification process, which places a significant burden on the end-user. Selecting a manufacturer-certified engine significantly reduces these responsibilities and ensures that the generator package is optimally designed and properly calibrated with the appropriate emissions control components.
The end-user must comply with the manufacturer’s requirements for installation, maintenance and engine adjustments. The user must also maintain:
- Proof of engine compliance
- Maintenance records
- Hours of operation in an emergency
- Hours of operation for readiness testing
- Hours of operation on back-up fuel
- Compliance updates/notifications
To learn more about the new EPA regulation and how Generac’s products satisfy the requirements, contact us.
Featured Project: Bland Correctional Center
Bland Correctional Center is located in a remote area of southwest Virginia at the end of a radial electrical distribution system. The center houses on average 620 inmates, and features a large agricultural business program, which provides meat and dairy to the state. The facility is subject to frequent ice storms and heavy snowfall and frequently experiences both brief and long-term power interruptions. The solution was to provide the facility with a minimum of 800kW of standby generation utilizing a 480V generator system, a 480V/12.47kV step up transformer and a 12.47kV service entrance rated automatic transfer switch.
The project was designed to add two 400kW generator sets to an existing 400kW generator set including complex paralleling switchgear. The proposed 3x400kW system would provide redundancy to meet the facility’s 800kW demand. National Power Corporation (NPC) was the selected supplier for the specified conventional paralleling system. NPC proposed a value engineered Modular Power System solution – including three new 400kW modules in lieu of two 400kW generator sets and conventional paralleling gear, at no additional cost to the customer. In a meeting with the warden, engineer, facility managers, and Virginia state representative, NPC presented the MPS solution explaining the benefits of the value-engineered solution. The installation was performed, and because paralleling switchgear was not required, start-up was performed in days rather than weeks. The installed system has served the facility many times during utility power outages. An added bonus for the customer was that the existing 400kW unit was deployed elsewhere. The units are under a five-year warranty and are in a preventative maintenance program, which includes quarterly visits and annual load bank testing.
Installing electrician, Parson and Lusk, said, “this installation was simple and straight forward. By not utilizing paralleling switchgear we greatly expedited the installation. The end user appreciates that during the critical winter months, the system provides N+2 redundancy, due to reduced facility loads, and during the summer, N+1 redundancy.”
The original installation was an outdoor installation but the customer decided to provide extra protection to the investment. An operator’s room and shelter was constructed to provide additional protection to the units and operating personnel.
