Pumps & Systems, October 2008
Here is a primer on the proper locations for surge protection in water and wastewater facilities.
A pump could be considered the heart of the water/wastewater system, moving the lifeblood of the business. Like your own heart, it is necessary to keep the pump in good shape and running well. And, like your heart, the pump can be susceptible to stoppage from an electric shock.
Either stoppage means a really bad day. This article will focus on protecting the pump system from electric shock, and leave heart health to you.
Choosing Surge Protection
As budgets are cut, it is necessary to focus on reducing costs. Unplanned downtime is an expense that can destroy a budget. Employing surge protection on vital equipment is a small cost compared to the high price of equipment repair and downtime. Motors typically can withstand a moderate electrical surge. The drive/inverter controlling the pump, however, can handle much less energy. Control circuitry provides a path for even small surges to cause downtime.
Applying the appropriate surge protection in the right location will prevent damage, but choosing the appropriate surge protection can be confusing. There is a wide selection of products, and the decision often is based on price. This can lead to a product being undersized or not appropriate for its application.
Once you decide protection is needed, it may be difficult to determine the right protection for your needs. There is no single specification that should be used as criteria for purchasing.
Rather than specifications, focus on the equipment's location, then determine the appropriate product to purchase. The installation location helps determine the choice of AC surge protection. The four locations are remote sites, service entrance, sub-panel and control cabinets. Each location requires different protection. If you know the location, you can apply the appropriate protection and not overspend on an oversized product.
Let's review the locations and explain what type of protection should be used for each.
Remote Sites
Pumps located at remote sites require a higher level of protection. Remote sites are facilities or structures not located in population centers, industrial parks or commercial centers. Some examples are water wells, irrigation pumps or filtering tanks at wastewater treatment plants. These sites are the most challenging to protect. They are subjected to large surge events, such as lightning. A well might be the best "ground" around and can be struck several times in one year. The pump and its supporting equipment are typically located close to the electrical service entrance.
Protecting remote sites from the damaging effect of large surge events requires protection that diverts lightning-induced surge currents, reduces the transient voltage to a safe level for the equipment and provides long-term protection without failure. Products designed for this application will use a "spark gap" with metal oxide varistors (MOVs) to keep voltage levels low and handle large surge currents. With proper grounding and bonding, surge protection designed for remote sites can provide years of protection.
Service Entrance
If the pump is located inside the facility, employ a two-level protection scheme. Surge protection installed at the service entrance provides the first level of defense against external surges. It creates a barrier that protects wiring and equipment within the facility. All downstream equipment will benefit from this protection. At the service entrance, large supply and surge currents are possible. Choose a unit that specifies that it is for use at the service entrance.
Within the Facility
Why would you want additional protection inside the facility if you already have protection installed at the service entrance? To make things just a little more complex, there are two different types of surges: external and internal.
Externally generated surges, such as lightning, send a large impulse down the power line. This energy will destroy the winding insulation in the motor, disabling the pump.
Internally generated surges are small, fast impulses caused by electrical equipment turning off and on. This type of surge is independent of weather.
Motors and drives commonly create these surges. Other equipment at the facility can impact the performance of critical pumps. These surges will slowly break down the winding insulation of the motor, eventually causing a failure unless caught by the predictive and preventive maintenance program.
Sub-Panel
Installing surge protection at the sub-panel feeding the pump or drive will supplement the protection at the service entrance and eliminate internally generated surges. Sub-panel protection is an important part of a cascade protection plan and will reduce unplanned downtime.
After determining the location for AC power surge protection on remote sites, service entrance and sub-panels, you need the voltage requirement. Once you list out the voltage, such as 480V/277V three-phase wye, you can select the product you need.
Control Cabinet
Pump systems with control cabinets will need protection designed for the control cabinet. Even with upstream protection, this area is very susceptible to damage. To protect the power side, install surge protection on the DIN rail. This protection ensures the AC to DC power supplies and PLC are protected.
Any signal/communication lines entering the pump control cabinet need to be protected. If surge protection is only on the AC power side, you are leaving a backdoor path for surges to enter your equipment and cause damage. A surge can travel on any wire, power or communication. A complete surge protection strategy addresses surges on all connections to equipment. It is important to investigate all signal lines such as digital/discrete, analog (4-20mA) coax, Ethernet, RS-485, etc. All of these represent paths that need protection.
For example, a float valve in a tank indicates when the pump should be turned off. This wire might leave the building and travel 50 yards away. A surge can travel down this wire and damage the PLC. Protection placed inside the control cabinet on this line will prevent downtime.
Proper Grounding and Bonding
Unfortunately, preventing surge damage is not as easy as simply buying and installing product. Before surge protection is installed, the electrical system must have proper grounding and bonding. The performance of the surge protection is tied to how well the electrical system is grounded and bonded. The higher the potential surge energy, the more critical this part of the installation becomes.
Surge protection diverts damaging energy to the ground. During a surge event, thousands of amps of electrical current can flow on the electrical wires. A surge event occurs in a short amount of time, about one microsecond. Fuses and circuit breakers will not provide protection from a surge, as they react much too slowly. Proper grounding and bonding will help the surge suppressor divert the energy away and improve the performance of the surge device. Like a clogged drain, the surge energy will back up if the grounding system is inadequate.
Extra ground rods are good additions, as long as they are bonded to the electrical system ground. The grounding wires should be slightly larger than those normally used. Bonding keeps the voltage differences from becoming too great within the system during a surge event or any fault condition. Make sure your installation meets National Electrical Code and any local regulations.
Conclusion
In the quest to reduce costs and eliminate downtown, surge protection is an important part of the pump system. Choosing the best surge protection begins with knowing the system voltage and the location of the pump. Picking a surge device designed for the location will provide the right protection for the application. The system voltage will enable you to select the right product. Reviewing and/or improving the grounding and bonding system also improves surge protection performance. Investment in surge protection can provide years of protection, saving your budget from large costs associated with unplanned downtime.