SubMonitor Pump Protection: Much More than an Overload Sensor

As all water systems professionals know, a submersible installation can be a tough environment for both pump and motor. Sometimes, no matter how professional the installation, things out of an installer’s control can severely damage a customer’s investment. The answer to such problems is the SubMonitor pump protection system, which offers state-of-the-art protection for Franklin 3- phase installations all the way from 5 through 200 Hp. The SubMonitor system keeps track of voltage and current, as well as motor temperature in motors equipped with Subtrol heat sensors. Introduced in 2004, SubMonitor protection will shut down a motor in the event of a variety of fault conditions including high voltage, low voltage, overload, underload, false start, current unbalance, overheating, phase loss and phase reversal. The unit is easy to set and read. And, one model covers all ratings – without rating inserts. Continue reading

Overload Protection for 3-Phase Motors

Several conditions can cause a motor to become overloaded. Examples include a bound pump, or a high or low voltage condition. When a motor becomes overloaded, the current (amps) increase, and can reach levels damaging to the motor. Therefore, a motor must be protected from an overload condition, and this is the job of the overload protector, sometimes just called the “overload”.

In a recent edition of the Franklin AID, we discussed overload protection in Franklin Electric single-phase motors. These motors contain “built-in” overload protection, either in the motor itself or in the Franklin Control Box, depending on the horsepower rating. In this issue, we will discuss 3-phase motor protection. Continue reading

Overload Protection of Three-Phase Submersible Motors

The characteristics of submersible motors are different from standard, above ground motors. Submersible motors require special overload protection. In order to properly protect a three-phase submersible motor, ambient-compensated, quick-trip overload protection must be used. This can be either a fixed heater or adjustable overload relay, as long as it is ambient-compensated and quick-trip. Franklin Electric?s Subtrol-Plus system can also be used to protect Subtrol-equipped motors.

Ambient-Compensated: Ambient-compensated overload protection must be used to maintain protection in both high and low air temperature areas. Three-phase pump panels are typically suitable for indoor and outdoor applications within temperatures of +14°F (-10°C) to +122°F (50°C). Pump panels should never be mounted in direct sunlight or high temperature locations as this will cause unnecessary tripping of overload protectors. A ventilated enclosure, painted white to reflect heat, is recommended for outdoor high temperature locations.

Quick-Trip: If the motor is stalled or the shaft cannot turn, the overload protector must trip quickly to protect the motor?s windings. In some areas, it is customary to specify that the overload must trip within 10 seconds with 500% normal current (IN). Quick-trip heaters and overload relays shown here, will respond within 10 seconds. Franklin?s Subtrol-Plus responds within 3 seconds. Heaters marked ?Standard Trip? are typically Class 20 or 20 second response time. Standard Trip, Class 20 and some Class 10 overloads will allow submersible motor burn-out before tripping. Quick-trip overload protection must be used.

The time-current trip curve, as shown in Figure 1, shows the response time for different classes of overloads under different running scenarios. The bottom axis of the chart shows different multiples of normal currents. The side axis shows ?Time? in seconds. The first bold vertical line represents the amperage if the power source single-phases on the motor side of the transformer (secondary side). This can occur if a fuse blows or a contact fails. This condition causes the normal line amperage to increase to 173% of normal in two phases and drop to zero in the third phase. The second bold vertical line represents the amperage if the power source single-phases on the incoming side of the transformer (primary side). This can occur if a power line is broken in a storm or car accident. This condition causes the normal line amperage to increase to 230% of normal in one phase and 115% of normal in two phases. The third vertical line represents a locked rotor or bound shaft condition. As you can see from the motor burnout curve or shaded area, the motor must be disconnected with a quick-trip device or severe motor damage can occur. The best protection, as the bold horizontal line shows, is Franklin?s Subtrol-Plus which disconnects the power within 3 seconds. Continue reading