Issued: 12/11

Supersedes: 3/09

Motor Thermal Protection GENERAL Overheating is the most common cause of electrical motor failure. Adequate protection against overheating is necessary for all electrical motors, and adequate protection against motor overloading (which causes overheating and mechanical strain) is required by the National Electrical Code - Art. 430, Part C. Motor protection against overloading can be done indirectly, controlling the cause - i.e. high running current for a prolonged period of time. or directly controlling the effect - high motor stator temperature, The second type of protection is provided for almost all Flygt pumps by inserting temperature sensors into the motor stator windings. THERMAL SWITCHES Flygt pump motors, with a few exceptions, are provided with two (2) or three (3) thermal switches embedded in the stator windings. The exceptions are: - some big pumps and hydroturbines; - warm liquid pumps (high temperature thermal switches are optional). DESCRIPTION Thermal switches installed into the pump motor stator windings are bimetallic, normally closed contact type. The device consists of a strip made of two dissimilar metals. The two metals have different temperature coefficient of expansion, so the heat causes the strip to bend. At a preset temperature the switch contact will open. As the stator cools down, the metallic strip returns to its original shape and the switch will reclose its contact. For different pumps/motors. Flygt uses a few different thermal switches, rated for different openclose temperatures. (See Technical Data.) INSTALLATION There are usually two (2) or three (3) switches inserted into the stator end turns during its production. The thermal switches are wired in series and connected by two (2) leads to the pump terminal board, (Terminals T1 and T2.) For small pumps, such as the 3085, the thermal switch connection to the cable is made with wire nuts. The closed/open status of the thermal switches is supervised by a relay or other device and the opening of one of the thermal switches shall trip the pump branch circuit breaker, or deenergize the motor starter, interrupting the power to the pump motor. The thermal switches in the stator will reset automatically, as described above, but to restart the motor a manual reset might be required, depending on the type of operation. If a leakage detector is also installed in the pump in conjunction with a Mini CAS supervision relay, the thermal switches are wired in series with the leakage sensor. (See Mini CAS manual-wiring diagram.) TECHNICAL DATA: Rated Voltage: 250 VAC Maximum Operating Voltage: 600 VAC Rated Current: 6.3 Amps @ 250 VAC, PF 0.60 Thermal Class F (+155°C) insulation CSA/UL Approved Operating Temperature: Opens at 110°C through 155°C, depending on pump type. Check the pump manual for the specific thermal switch temperature rating.

Issued: 3/09

Supersedes:

Motor Thermal Protection TESTING The thermal switches have normally closed contacts and are wired in series. For a cold motor, between the leads connecting the thermal switch, the resistance measured with a regular ohm meter should be under 1 ohm. If the thermal switch resistance is measured at the end of the cable, cable leads’ resistance should be considered in series with the switches when reading the meter. An open circuit or high ohms’ reading for the cold motor indicates a defective thermal switch or a loose connection. PTC THERMISTORS Older Flygt pumps and some FM-Approved, explosion-proof pumps can use PTC (positive temperature coefficient) thermistors for stator over temperature protection, instead of thermal switches. DESCRIPTION A PTC thermistor increases its internal resistance when temperature is increased. The thermistors used in above-mentioned pumps are non-linear type, which means that for a preset temperature. thermistor resistance will suddenly begin to increase rapidly. (See attached Resistance/Temperature curve.)

Non-Linear PTC Thermistor Curve

3K

Point of activation

2K

1K 700

Resistance - Ohms

500

250

100

Switch-over Point

50

20

˚F

68

104

140

˚C

20

40

60

176 201 80

94

248

284

120

140

Temperature

INSTALLATION Stator thermistor circuits use three thermistors connected in series. The same type of thermistors are also used for measuring the bearing temperature. For temperature supervision, the thermistors are wired in the control panel to special thermistor relays - one for stator temperature and one for bearing temperature. The relay will react to the sudden change in thermistor temperature and trip the pump circuit breaker or de-energize pump motor starter. TECHNICAL DATA Stator temperature PTC thermistors - three (3) thermistors connected in series. Total resistance at 25°C (77°F) - 150-300 ohms not to exceed 750 ohms. Bearing temperature PTC thermistor - one (1) each - Resistance 50 - 100 ohms at 25°C (77°F) - not to exceed 250 ohms.

Issued: 3/09

Supersedes:

Motor Thermal Protection TESTING CAUTION: MAXIMUM TEST VOLTAGE FOR PTC THERMISTORS IS 2.5 VOLTS D.C. Application of more than 2.5 volts will destroy the thermistors. At room temperature, PTC thermistor resistance should be within the above limits. PT 100 SENSOR FOR BEARING TEMPERATURE SUPERVISION DESCRIPTION PT 100 sensors are Resistance Temperature Detectors (RTD) made of platinum. The resistance of platinum is linear with temperature over a wide range and they are thus capable of a great temperature accuracy. “100” refers to the sensor resistance at 0°C (32°F), which is 100 ohms. Used together with the Flygt MAS 711 pump monitoring system, the PT 100 sensor provides an accurate indication and permanent monitoring of the bearing temperature.

Linear PT 100 Lower Bearing Sensor Curve 160

150

Resistance - Ohms

140

130

120

110

100

˚F

68

104

140

176

212

248

284

˚C

20

40

60

80

100

120

140

Temperature

Issued: 3/09

Supersedes:

Motor Thermal Protection INSTALLATION One PT 100 sensor is installed into the bearing housing of the big pumps and hydroturbines. Standard connection to the MAS 711 is made with two (2) wires. As the wires’ resistance adds to sensor resistance, a long cable run from the pump terminal board to the supervision relay will change the temperature reading. Example: At 90°C (194°F), PT 100 resistance is 134.7 ohms. A two-wire connection with AWG #14 cable, 1,000 ft. Long, will add: 2 x 3.07 x 1.0 = 6.14 ohms. Total resistance is now 140.84 ohms, which corresponds to 105°C temperature for PT 100 itself. If the MAS 711 unit is set for l00°C, the pump will be tripped even if the bearing temperature is still acceptable. To avoid having this happen, the MAS 711 must be programmed with a resistance offset to compensate for lead resistance. If the PT100 has three leads, connect red lead(s) to one measuring terminal point and blue lead(s) to the other measuring terminal point. Terminal points can be found in the MAS 711 Installation Manual. TECHNICAL DATA Maximum measuring voltage: 2.5V

Issued: 3/09

Supersedes:

Motor Thermal Protection Temperature/Resistance Table for Platinum PT 100 Sensors °C -200 -195 -190 -185 -180 -175 -170 -165 -160 -155 -150 -145 -140 -135 -130 -125 -120 -115 -110 -105 -100 -95 -90 -85 -80 -75 -70 -65 -60 -55 -50 -45 -40 -35 -30 -25 -20 -15 -10 -5 0 5 10 15

Ω 18.52 20.68 22.83 24.97 27.10 29.22 31.33 33.44 35.54 37.64 39.72 41.80 43.88 45.94 48.00 50.06 52.11 54.15 56.19 58.23 60.26 62.28 64.30 66.31 68.33 70.33 72.33 74.33 76.33 78.32 80.31 82.29 84.27 86.25 88.22 90.19 92.16 94.12 96.09 98.04 100.00 101.95 103.90 105.85

°C 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 110 115 120 125 130 135 140 145 150 155 160 165 170 175 180 185 190 195 200 205 210 215 220 225 230 235

Ω

°C

107.79 109.73 111.67 113.61 115.54 117.47 119.40 121.32 123.24 125.16 127.08 128.99 130.90 132.80 134.71 136.61 138.51 140.40 142.29 144.18 146.07 147.95 149.83 151.71 153.58 155.46 157.33 159.19 161.05 162.91 164.77 166.63 168.48 170.33 172.17 174.02 175.86 177.69 179.53 181.36 183.19 185.01 186.84 188.66

240 245 250 255 260 265 270 275 280 285 290 295 300 305 310 315 320 325 330 335 340 345 350 355 360 365 370 375 380 385 390 395 400 405 410 415 420 425 430 435 440 445 450 455

Ω 190.47 192.29 194.10 195.91 197.71 199.51 201.31 203.11 204.90 206.70 208.48 210.27 212.05 213.83 215.61 217.38 219.15 220.92 222.69 224.45 226.21 227.96 229.72 231.47 233.21 234.96 236.70 238.44 240.18 241.91 243.64 245.37 247.09 248.81 250.53 252.25 253.96 255.67 257.38 259.08 260.78 262.48 264.18 265.87

°C 460 465 470 475 480 485 490 495 500 505 510 515 520 525 530 535 540 545 550 555 560 565 570 575 580 585 590 595 600 605 610 615 620 625 630 635 640 645 650 655 660

TESTING: CAUTION: MAXIMUM TEST VOLTAGE FOR PT 100 SENSOR IS 2.5 VDC.

Ω 267.56 269.25 270.93 272.61 274.29 275.97 277.64 279.31 280.98 282.64 284.30 285.96 287.62 289.27 290.92 292.56 294.21 295.85 297.49 299.12 300.75 302.38 304.01 305.63 307.25 308.87 310.49 312.10 313.71 315.31 316.92 318.52 320.12 321.71 323.30 324.89 326.48 328.06 329.64 331.22 332.79