{"id":262,"date":"2026-07-10T06:03:58","date_gmt":"2026-07-10T06:03:58","guid":{"rendered":"https:\/\/industrialelectricmotor.net\/?p=262"},"modified":"2026-07-10T06:03:58","modified_gmt":"2026-07-10T06:03:58","slug":"inverter-duty-motor-for-hvac-fan-and-pump","status":"publish","type":"post","link":"https:\/\/industrialelectricmotor.net\/sk\/inverter-duty-motor-for-hvac-fan-and-pump\/","title":{"rendered":"Inverter-Duty Motor for HVAC Fan and Pump"},"content":{"rendered":"
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Korea Ever-Power \u00b7 YVF2 Series \u00b7 HVAC Drive Application Guide<\/span><\/p>\n

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Inverter-Duty Motor for HVAC Fan and Pump:
\nWhy VFD Drives Need a Special Motor<\/span><\/h1>\n

A standard three-phase induction motor connected to a variable frequency drive (VFD) in an HVAC fan or pump application will typically fail within 2 to 5 years from winding insulation breakdown, bearing current damage, or overheating at low speed \u2014 none of which would occur if the motor were running on a fixed-frequency sinusoidal supply. Korea Ever-Power YVF2 inverter-duty motors are engineered to address all three failure modes, making them the correct and safe specification for all HVAC VFD applications above 0.75 kW.<\/p>\n

IC416 Forced Cooling<\/span>
\nClass H Insulation<\/span>
\nBearing Current Protection<\/span>
\nEnergy Saving P \u221d n\u00b3<\/span>
\n0.75\u2013200 kW<\/span><\/div>\n<\/div>\n<\/div>\n

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51%<\/div>\n
Power saved at 80% fan speed<\/div>\n<\/div>\n
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1\u20133 yr<\/div>\n
Typical VFD payback period on HVAC fan<\/div>\n<\/div>\n
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Class H<\/div>\n
Insulation vs Class F in standard motors<\/div>\n<\/div>\n
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IC416<\/div>\n
Forced blower: full torque from 0 to 60 Hz<\/div>\n<\/div>\n
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PTC<\/div>\n
Thermistor winding protection standard<\/div>\n<\/div>\n<\/div>\n

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\"YVF2<\/p>\n
Korea Ever-Power YVF2 series inverter-duty motor \u2014 the independent blower on the non-drive end (visible at rear) provides IC416 forced ventilation that maintains full cooling airflow regardless of motor speed, eliminating the overheating risk that makes standard IC411 self-ventilated motors unsuitable for VFD operation at low speed in HVAC fan and pump drives.<\/div>\n<\/div>\n

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Contents<\/div>\n
1. Energy Saving: The Case for VFD on HVAC<\/a>
\n2. Why Standard Motors Fail on VFD<\/a>
\n3. IC416 vs IC411: Cooling at Low Speed<\/a>
\n4. Class H Insulation for VFD Voltage Spikes<\/a>
\n5. Bearing Current Protection<\/a>
\n6. YVF2 Specifications for HVAC<\/a>
\n7. HVAC Applications<\/a>
\n8. Frequently Asked Questions<\/a><\/div>\n<\/div>\n

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1. Energy Saving: The Case for VFD on HVAC Fan and Pump Drives<\/h2>\n

HVAC fans and chilled water pumps in commercial and industrial buildings are typically designed to meet peak load conditions \u2014 the hottest day of the year or the maximum occupied building load. For 70 to 90 percent of operating hours, the actual demand is significantly below peak, yet a fixed-speed motor with a damper or valve runs at full power and wastes the excess capacity across a restriction. VFD speed control eliminates this waste by matching fan or pump speed to actual demand.<\/p>\n

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Worked Energy Saving Example \u2014 AHU Supply Fan<\/div>\n
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Without VFD (damper control):<\/div>\n
Motor: 22 kW at full speed, 8,000 h\/yr
\nAverage load: 75% of peak
\nAnnual consumption: 22 \u00d7 8,000 = 176,000 kWh<\/strong>
\nAnnual cost at $0.13\/kWh = $22,880<\/strong><\/div>\n<\/div>\n
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With VFD + YVF2 motor (speed control):<\/div>\n
Average speed: 85% of full speed
\nAverage power: 22 \u00d7 (0.85)\u00b3 = 13.5 kW
\nAnnual consumption: 13.5 \u00d7 8,000 = 108,000 kWh<\/strong>
\nAnnual cost = $14,040 \u2014 saving $8,840\/yr<\/strong><\/div>\n<\/div>\n<\/div>\n
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Payback period: VFD system cost $4,500 \u00f7 $8,840\/yr saving = 0.51 years (6 months)<\/div>\n<\/div>\n<\/div>\n

This example illustrates why VFD speed control on HVAC fans and pumps typically has a payback period of 6 months to 2 years \u2014 making it one of the highest-return energy efficiency investments available in building services. The key is pairing the VFD with a YVF2 inverter-duty motor, not a standard Y2 motor, to ensure reliable long-term operation.<\/p>\n<\/div>\n

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2. Why Standard Motors Fail on VFD Drives<\/h2>\n

A standard Y2 motor (IC411 self-ventilated, Class F insulation) connected directly to a VFD without motor-specific protection will experience three failure mechanisms that do not occur on sinusoidal fixed-frequency supply:<\/p>\n

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1. Insulation Breakdown from Voltage Spikes<\/div>\n

VFD output is a pulse-width-modulated (PWM) waveform with switching voltage spikes of 1,000 to 1,600 V (depending on cable length and VFD switching frequency) that repeat at the carrier frequency of 2 to 16 kHz. Standard Class F winding insulation, designed for sinusoidal supply, degrades rapidly under repeated high-frequency voltage spikes. Partial discharge in the winding insulation progressively erodes the conductor insulation, causing turn-to-turn shorts within 2 to 4 years of VFD operation without adequate motor insulation specification.<\/p>\n<\/div>\n

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2. Overheating at Low Speed<\/div>\n

Standard IC411 motors use a shaft-mounted fan to cool the stator and winding \u2014 the cooling airflow is proportional to shaft speed. At 25 Hz (50% of rated speed), the cooling fan provides only approximately 25% of full-speed cooling airflow. However, at 25 Hz the motor still produces rated torque and therefore approximately 50% of rated power, which generates substantial heat that the fan cannot adequately dissipate. The winding temperature rises above the Class F limit, accelerating insulation ageing by 2x for every 10 K excess temperature (Montsinger Rule).<\/p>\n<\/div>\n

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3. Bearing Current Damage<\/div>\n

VFD PWM switching creates capacitive coupling between stator windings and the rotor shaft, inducing a common-mode voltage on the shaft. This shaft voltage discharges through the motor bearings (the lowest-resistance path to ground), causing high-frequency electrical discharge machining (EDM) of the bearing races and balls. Bearing current damage produces characteristic frosting and fluting patterns on the bearing race surface, which leads to increased vibration and bearing failure within 6 to 18 months on standard unprotected bearings running on high-carrier-frequency VFDs.<\/p>\n<\/div>\n<\/div>\n<\/div>\n

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3. IC416 vs IC411: Cooling at Low Speed<\/h2>\n

IEC 60034-6 defines motor cooling circuit designations. IC411 is the standard self-ventilated cooling circuit \u2014 the motor cools itself through a shaft-mounted fan. IC416 is the forced-ventilated cooling circuit \u2014 a separate independently powered blower motor provides constant cooling airflow regardless of main motor speed.<\/p>\n

\n\n\n\n\n\n\n\n\n\n\n
Property<\/th>\nIC411 (Standard Y2)<\/th>\nIC416 (YVF2 Series)<\/th>\n<\/tr>\n<\/thead>\n
Cooling fan drive<\/td>\nShaft-mounted (speed dependent)<\/td>\nIndependent blower motor (constant)<\/td>\n<\/tr>\n
Cooling at 25 Hz (50% speed)<\/td>\n~25% of rated airflow<\/td>\n100% of rated airflow<\/td>\n<\/tr>\n
Cooling at 5 Hz (10% speed)<\/td>\n~2% of rated airflow \u2014 critical<\/td>\n100% of rated airflow<\/td>\n<\/tr>\n
Rated torque at low speed<\/td>\nDerate below 30 Hz<\/td>\nFull rated torque from 0 to rated frequency<\/td>\n<\/tr>\n
Static holding torque (0 Hz)<\/td>\nNo cooling \u2014 not suitable<\/td>\nFull cooling \u2014 static holding possible<\/td>\n<\/tr>\n
VFD suitability<\/td>\nNot recommended below 50 Hz continuous<\/td>\nDesigned for 0\u2013120 Hz VFD operation<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n

For HVAC fan drives that operate regularly below 40 Hz (80% of rated speed) \u2014 which is the normal operating range for most VFD-controlled AHU fans and cooling tower fans outside of peak load conditions \u2014 IC416 forced cooling is not optional. It is a fundamental requirement for safe and reliable long-term operation.<\/p>\n<\/div>\n

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4. Class H Insulation for VFD Voltage Spikes<\/h2>\n
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The YVF2 series uses Class H winding insulation (maximum continuous temperature 180\u00b0C) with a VFD-duty formulation that includes enhanced partial discharge resistance. Class H insulation in the YVF2 provides two layers of additional protection compared to the Class F insulation in a standard Y2 motor:<\/p>\n

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Higher voltage spike tolerance<\/div>\n

VFD-duty Class H insulation in the YVF2 is formulated with a higher dielectric strength and a higher partial discharge inception voltage than standard Class F insulation. It is rated to withstand repetitive voltage spikes of up to 1,600 V peak (dV\/dt up to 5,000 V\/\u03bcs) without progressive insulation breakdown \u2014 matching the output characteristics of modern IGBT-based VFDs operating with cable runs up to approximately 50 m without additional output filtering.<\/p>\n<\/div>\n

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Thermal reserve at operating temperature<\/div>\n

Even with IC416 forced cooling, operating a motor at low speed with full torque generates more heat per unit of output power than at rated speed. The 25 K thermal reserve of Class H over Class F means the YVF2 winding runs at a lower fraction of its thermal limit under the same operating conditions, extending insulation life in accordance with the Montsinger Rule.<\/p>\n<\/div>\n<\/div>\n<\/div>\n

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Insulation Comparison<\/div>\n\n\n\n\n\n\n\n\n
Property<\/th>\nClass F<\/th>\nClass H<\/th>\n<\/tr>\n<\/thead>\n
Max temp<\/td>\n155\u00b0C<\/td>\n180\u00b0C<\/td>\n<\/tr>\n
Thermal reserve*<\/td>\n15 K<\/td>\n40 K<\/td>\n<\/tr>\n
Relative life at 40\u00b0C ambient<\/td>\n1\u00d7<\/td>\n8\u00d7<\/td>\n<\/tr>\n
VFD duty rating<\/td>\nStandard<\/td>\nVFD-duty<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n
*Reserve above Class B rise (80 K) at 40\u00b0C ambient<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n

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5. Bearing Current Protection<\/h2>\n

The YVF2 series addresses VFD bearing current damage through a combination of bearing selection, insulation, and grounding design. The severity of bearing current depends on motor frame size, VFD carrier frequency, and cable length. Korea Ever-Power applies the following protection measures in the YVF2 series:<\/p>\n

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Insulated Non-Drive-End Bearing (Frame 180+)<\/div>\n

For YVF2 motors in frames 180M and above, the non-drive-end (NDE) bearing is fitted in an insulated housing that breaks the shaft-to-bearing-to-frame current path. Bearing current is forced to find an alternative path to earth that does not include bearing surfaces, protecting the drive-end bearing from the bulk of the circulating current.<\/p>\n<\/div>\n

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Shaft Grounding Ring (Optional)<\/div>\n

A conductive microfibre shaft grounding ring provides a low-impedance path for common-mode shaft voltage to discharge to earth without passing through the bearing. Recommended for YVF2 motors above 11 kW on VFDs with carrier frequencies above 4 kHz, or for installations with long motor cables (above 30 m). Available as an option from Korea Ever-Power.<\/p>\n<\/div>\n

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VFD-Side dV\/dt Filter (Recommended for Long Cables)<\/div>\n

A dV\/dt output filter on the VFD reduces the rate of voltage rise of the PWM pulses, limiting peak overvoltage at the motor terminals. For motor-to-VFD cable runs above 50 m, a dV\/dt filter reduces peak voltage at motor terminals to below the YVF2 insulation limit regardless of VFD switching frequency. Korea Ever-Power recommends VFD-side filters for HVAC fan installations with long cable routes from central VFD panels to remote AHUs.<\/p>\n<\/div>\n<\/div>\n<\/div>\n

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6. YVF2 Specifications for HVAC Applications<\/h2>\n
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The Korea Ever-Power YVF2 series is a purpose-designed inverter-duty motor for VFD applications in HVAC and industrial systems. The YVF2 is available in the VFD inverter-duty motor product section<\/a> across the 0.75 to 200 kW power range in 2-pole and 4-pole configurations. The 4-pole (1,450 rpm) configuration is the standard for AHU fans, cooling tower fans, and chilled water pumps; the 2-pole (2,900 rpm) configuration is used for high-speed centrifugal fans and process pumps where the pump or fan is designed for 2,900 rpm operation.<\/p>\n<\/div>\n

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YVF2 Key Specifications<\/div>\n\n\n\n\n\n\n\n\n\n\n
Power range<\/td>\n0.75\u2013200 kW<\/td>\n<\/tr>\n
Cooling<\/td>\nIC416 forced ventilation<\/td>\n<\/tr>\n
Insulation<\/td>\nClass H, VFD-duty<\/td>\n<\/tr>\n
Speed range<\/td>\n0\u2013120 Hz VFD supply<\/td>\n<\/tr>\n
Protection<\/td>\nIP54 standard<\/td>\n<\/tr>\n
PTC thermistors<\/td>\nStandard \u2014 connect to VFD PTC input<\/td>\n<\/tr>\n
Voltage spike rating<\/td>\nUp to 1,600 V peak<\/td>\n<\/tr>\n
Poles<\/td>\n2P (2,900 rpm) \/ 4P (1,450 rpm)<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n

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7. HVAC Applications<\/h2>\n\n\n\n
\"YVF2<\/p>\n
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Chilled Water and Condenser Water Pumps<\/div>\n

Primary and secondary chilled water pumps in central plant HVAC are the largest single energy consumer in most commercial buildings. YVF2 4-pole 7.5 to 75 kW paired with a building management system (BMS) controlled VFD delivers variable primary flow (VPF) control, reducing pump energy by 40 to 60 percent compared to constant volume systems. The VFD modulates pump speed to maintain differential pressure set point across the distribution system as zone valve positions change with load variation.<\/p>\n<\/div>\n<\/td>\n

\"YVF2<\/p>\n
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Air Handling Unit (AHU) Supply and Return Fans<\/div>\n

Supply and return fans in large AHUs serving commercial offices, hospitals, data centres, and industrial facilities are the primary application for YVF2 motors in HVAC. Fan motors from 7.5 to 90 kW, VFD-controlled from a BMS or stand-alone HVAC controller to maintain supply air temperature and duct static pressure set points. Variable air volume (VAV) systems reduce fan speed as zone dampers close, saving fan energy proportionally to the cube of speed reduction.<\/p>\n<\/div>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

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Cooling Tower Fan<\/div>\n

Induced-draft cooling tower fans use YVF2 4-pole 3.0 to 30 kW motors. VFD control modulates fan speed to maintain condenser water supply temperature, reducing fan energy by 50 to 70 percent compared to fixed-speed two-speed motors. Outdoor installation requires IP55; Class H insulation is important as the motor discharges warm humid air from the tower.<\/p>\n<\/div>\n

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Boiler Feed Pump<\/div>\n

Boiler feed pumps in industrial steam systems use YVF2 2-pole or 4-pole motors in 3.0 to 55 kW range. VFD control modulates feed flow to match steam demand, replacing the drum level control valve with direct speed control and saving 20 to 40 percent of pump energy in variable-demand steam systems.<\/p>\n<\/div>\n

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Exhaust and Extract Fan<\/div>\n

Kitchen exhaust, laboratory fume cupboard extract, and car park ventilation fans use YVF2 motors with CO or CO\u2082 demand-controlled VFD operation. Fan speed reduces to minimum during low-occupancy periods, saving 40 to 60 percent of fan energy in commercial building and public facility ventilation systems.<\/p>\n<\/div>\n

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Compressor Inlet Guide Vane<\/div>\n

Centrifugal chiller compressor capacity control using VFD-driven guide vane actuator motors or direct compressor VFD drive. YVF2 motors 0.75 to 7.5 kW for guide vane actuator duty. Full compressor VFD drive uses YVF2 at the rated compressor motor size, typically 30 to 200 kW for large chillers.<\/p>\n<\/div>\n<\/div>\n<\/div>\n

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\"Korea<\/p>\n

Precision Machining<\/div>\n<\/div>\n
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\"Korea<\/p>\n

VFD Performance Test<\/div>\n<\/div>\n
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\"Korea<\/p>\n

CE and ISO Certified<\/div>\n<\/div>\n
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\"Korea<\/p>\n

Global HVAC Customers<\/div>\n<\/div>\n<\/div>\n

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8. Frequently Asked Questions<\/h2>\n
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Can I add a VFD to an existing standard Y2 motor on my AHU fan without changing the motor?<\/div>\n<\/div>\n
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You can operate a standard Y2 motor on a VFD for short periods, but for continuous HVAC duty this approach has significant long-term risks. If the fan only operates between 40 and 50 Hz (80 to 100% of rated speed), the cooling reduction at low speed is modest and the standard insulation may not be seriously stressed, depending on cable length and VFD carrier frequency. However, any time the fan operates below 30 Hz for sustained periods \u2014 which is typical in variable air volume systems \u2014 the standard IC411 cooling becomes inadequate and the insulation is stressed by repeated PWM voltage spikes. For a reliable retrofit of an existing fan to VFD control, the preferred approach is to replace the Y2 motor with a YVF2 at the same frame size and power rating and connect the new motor to the VFD. The incremental cost of specifying a YVF2 over a Y2 is typically recovered within 6 to 12 months through extended motor service life alone.<\/p>\n<\/div>\n<\/div>\n

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Do PTC thermistors in the YVF2 motor connect directly to the VFD?<\/div>\n<\/div>\n
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Yes \u2014 most modern VFDs include a PTC thermistor input circuit that monitors the motor winding temperature directly. The YVF2 is supplied with three PTC thermistors embedded in the stator winding (one per phase) connected to a terminal in the motor terminal box, separate from the main power terminals. Connect the PTC circuit to the VFD PTC input and configure the VFD to alarm and trip if the thermistor resistance exceeds the 3.3 k\u03a9 trip threshold (which corresponds to a winding temperature approaching the Class H thermal limit). This provides a direct thermal protection that supplements the VFD electronic overload \u2014 the PTC protects against conditions that the electronic overload may not detect, such as blocked cooling air intake or sustained operation at low speed with high torque demand. Always enable the PTC protection \u2014 do not leave it disconnected.<\/p>\n<\/div>\n<\/div>\n

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What minimum speed can I run a YVF2 motor at for continuous HVAC fan duty?<\/div>\n<\/div>\n
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The YVF2 with IC416 cooling can produce full rated torque at any speed from near-zero to 120 Hz, because the blower maintains full airflow independently of motor shaft speed. From a thermal perspective, there is no minimum speed limit for continuous operation. From a practical HVAC control perspective, centrifugal fans become inefficient below approximately 20 to 25 Hz (40 to 50% of rated speed) because the fan operates far from its design point \u2014 the flow drops approximately to the cube root of the power, but the system resistance may cause the fan to stall at very low speeds. Most HVAC VFD control systems set a minimum frequency of 20 to 25 Hz for centrifugal fan applications, which corresponds to 40 to 50% of rated speed, to maintain stable fan operation and adequate ventilation rates above the minimum air change requirement for the served space.<\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n

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Korea Ever-Power \u00b7 YVF2 Series \u00b7 HVAC VFD Motor<\/div>\n

Specifying a VFD Motor for Your HVAC Fan or Pump?<\/h2>\n

Korea Ever-Power YVF2 series: IC416 blower, Class H VFD-duty insulation, PTC thermistors, 0.75\u2013200 kW, 2-pole and 4-pole. The correct motor for every HVAC VFD application.<\/p>\n

View YVF2 Motor Range<\/a><\/p>\n<\/div>\n<\/div>\n

Edited by Cxm<\/p>\n<\/div>","protected":false},"excerpt":{"rendered":"

Korea Ever-Power \u00b7 YVF2 Series \u00b7 HVAC Drive Application Guide Inverter-Duty Motor for HVAC Fan and Pump: Why VFD Drives Need a Special Motor A standard three-phase induction motor connected to a variable frequency drive (VFD) in an HVAC fan or pump application will typically fail within 2 to 5 years from winding insulation breakdown, […]<\/p>","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_et_pb_use_builder":"","_et_pb_old_content":"","_et_gb_content_width":"","footnotes":""},"categories":[28],"tags":[],"class_list":["post-262","post","type-post","status-publish","format-standard","hentry","category-industrial-electric-motor"],"_links":{"self":[{"href":"https:\/\/industrialelectricmotor.net\/sk\/wp-json\/wp\/v2\/posts\/262","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/industrialelectricmotor.net\/sk\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/industrialelectricmotor.net\/sk\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/industrialelectricmotor.net\/sk\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/industrialelectricmotor.net\/sk\/wp-json\/wp\/v2\/comments?post=262"}],"version-history":[{"count":1,"href":"https:\/\/industrialelectricmotor.net\/sk\/wp-json\/wp\/v2\/posts\/262\/revisions"}],"predecessor-version":[{"id":265,"href":"https:\/\/industrialelectricmotor.net\/sk\/wp-json\/wp\/v2\/posts\/262\/revisions\/265"}],"wp:attachment":[{"href":"https:\/\/industrialelectricmotor.net\/sk\/wp-json\/wp\/v2\/media?parent=262"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/industrialelectricmotor.net\/sk\/wp-json\/wp\/v2\/categories?post=262"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/industrialelectricmotor.net\/sk\/wp-json\/wp\/v2\/tags?post=262"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}