Cúlóir Chosanta: Cineálta, Deifecte agus Aicmeanna
Is ionadúr cosaint mhótar meicniúil agus modhanna é scéim chosaint mhótar atá ann chun córas mótar leictreach a chosaint ó dhaoine de fholachtaí agus damáiste. Is gníomhach tábhachtach é an t-mótar leictreach i go leor úsáidí tionsclaíocha agus dhaonlathacha, ó earráin beaga go dtí máistir mhóra. Mar sin, is tábhachtach é a chinntiú go bhfuil an t-mótar agus a chóras ag obair go maith agus go sábhálta.
Sa chuid seo, pléifear na cineálacha folachtaí mótar, na cineálacha comhdhalaí cosaint mhótar, agus conas roghnú iad de réir Córas Náisiúnta Leictre (NEC) agus carachtaristíochtaí an mhótar.
Cad é Folach Mótar?
Is staid é folach mótar a chuirpíonn go n-oibríonn an t-mótar gan réiteach nó faoi bhriseadh. Is féidir folachtaí mótar a ghradú i dteochar cathracha:
Folachtaí seachtracha: Is folachtaí é seo atá ag teacht ón gcóras soláthar leictreach nó ón mbhall a bhfuil an t-mótar ceangailte leis. Seo roinnt eiseamláirí de folachtaí seachtracha:
Voltáid neamhchoimeádach: Téann sé seo ar bun nuair nach bhfuil na voltáid trífhásacha cothrom i mheastachán nó i ngearrleathan. Is féidir leis seo cinnseáil neamhchoimeádach a chruthú sa mhótar, a chur ar aird a chur ar thábhacht, teocht, agus pulsáil torca.
Iolrá: Téann sé seo ar bun nuair a titheann an voltáid soláthair faoi luach reatha an mhótar. Is féidir leis seo torcas lag, cinnseáil ard, agus teocht an mhótar a chur ar a mhéid.
Seicheamh fásach in aisce: Téann sé seo ar bun nuair a dtrialtar ord na fásachaí soláthara. Is féidir leis seo tuairisc in aisce an mhótar a chruthú, rud a d'fhéadfadh briseadh a dhéanamh ar an mbhall nó ar an t-mótar féin.
Cailltear coibhneas: Téann sé seo ar bun nuair a chailltear an gluais magnaiticiúil agus an tréimhse soláthair ag mótar síochánta. Is féidir leis seo slip míchruinn, lorg, agus instabilitate an mhótar a chruthú.
Folachtaí intíre: Is folachtaí é seo atá ag teacht ón t-mótar nó ón mbhall a bhíonn á imirt aige. Seo roinnt eiseamláirí de folachtaí intíre:
Béarach: Téann sé seo ar bun nuair a chuirtear an béarach a thacaíonn an shaol an mhótar as feidhm nó a chuirtear amach mar gheall ar fhricse, fadhb folaíochta, nó strus meicniúil. Is féidir leis seo fuaim, vibráid, misalinneacht saol, agus stalling an mhótar a chruthú.
Teocht: Téann sé seo ar bun nuair a thagann teocht an mhótar os cionn a teorainn thermach mar gheall ar overloading, fadhb folaíochta, coinníollacha comhsholas, nó briseadh insuláide. Is féidir leis seo cur ar a mhéid insuláide, briseadh windings, agus laghdú oiriúnach an mhótar.
Briseadh windings: Téann sé seo ar bun nuair a bhíonn an windings an mhótar short-circuited nó open-circuit mar gheall ar briseadh insuláide, strus meicniúil, nó folachtaí seachtracha. Is féidir leis seo spáir, tobac, tine, agus cailltear torcas an mhótar.
Fault talún: Téann sé seo ar bun nuair a thagann fásach conductor an mhótar i dteagmháil le cuid talún den chóras nó an t-equipment. Is féidir leis seo fault currents ard, briseadh insuláide agus equipment, agus forbróga shock.
D'fhéadfadh folachtaí mótar a bheith leis na huafás do chumas, sláinte, agus aois an mhótar agus a chóras. Mar sin, is tábhachtach é a aimsiú agus a chosaint ina ndiaidh using devices and methods appropriate.
Cad é Comhad Cosaint Mótar?
Is comhad é comhad cosaint mhótar a monatóireann agus a chontrollann paraiméadar amháin nó breise den t-mótar nó a chóras, mar shampla cinnseáil, voltáid, teocht, luas nó torcas. Is é an príomhaidhm comhad cosaint mhótar ná stop a chur leis nó laghdú a dhéanamh ar dhamáiste don t-mótar agus a chóras i gcás folachta nó staid neamhchoimeádach.
Tá comhaid cosaint mhótar éagsúla ann ag brath ar a ngníomh, prionsabal, agus úsáid. Seo roinnt cineál éagsúla coitianta:
Fuses: Is comhaid iad seo a chuirtear isteach i gcothrom an chórais nuair a théann cinnseáil ard tríothu mar gheall ar short circuit nó overloading. Consist of a metal strip or wire that melts when heated by the fault current. Fuses are simple, cheap, and reliable devices that provide fast protection against short-circuits. However, they have some disadvantages, such as:
Ní féidir iad a athúsáid agus ní mian go mbeadh orthu a athsholáthar tar éis gach oibriú.
Ní thugann siad cosaint in aghaidh overloads nó under-voltages.
Ní thugann siad léarscáil nó aonchor an folachta.
Circuit breakers: Is comhaid iad seo a chuirtear isteach i gcothrom an chórais nuair a téann cinnseáil ard tríothu mar gheall ar short circuit nó overloading. Consist of a pair of contacts that open or close by an electromechanical mechanism triggered by a sensing element. Circuit breakers are more advanced than fuses as they provide the following:
Athúsáid agus resetability tar éis gach oibriú.
Cosaint in aghaidh overloads agus under-voltages trí a trip settings a chur in eagar.
Léarscáil agus aonchor an folachta trí oibriú manual nó uathoibríoch.
Overload relays: Is comhaid iad seo a chuirtear isteach i gcothrom an chórais nuair a téann cinnseáil ard tríothu mar gheall ar overload. Consist of a sensing element that measures the current and a contact that opens or closes by an electromechanical or electronic mechanism. Overload relays are designed to protect motors from overheating and insulation damage due to prolonged overloads or unbalanced voltages. There are two main types of overload relays:
Faster response and better protection against short-circuit currents or ground faults.
Immunity to ambient temperature and no need for adjustment.
Higher accuracy and repeatability due to digital processing.
Additional features such as phase loss detection, reverse rotation detection, communication, and diagnostics.
They are slow to respond and may not protect against short-circuit currents or ground faults.
They are affected by ambient temperature and may need to be adjusted accordingly.
They have limited accuracy and repeatability due to mechanical wear and tear.
Thermal overload relays: These are devices that use a bimetallic strip or a heating element to sense the temperature rise of the motor current. When the current exceeds the preset value, the thermal element bends or melts, causing the contact to open or close. Thermal overload relays are simple, cheap, and reliable devices that provide inverse time protection, meaning they trip faster for higher overloads. However, they have some disadvantages, such as:
Electronic or digital overload relays: These are devices that use a current transformer or a shunt resistor to measure the motor current and a microprocessor or a solid-state circuit to control the contact. When the current exceeds the preset value, the electronic element sends a signal to open or close the contact. Electronic or digital overload relays are more advanced than thermal overload relays as they provide:
Differential protection relays: These are devices that compare the currents at the input and output terminals of the motor or its winding. When the difference between the currents exceeds a certain value, indicating a winding fault, the relay trips the circuit. Differential protection relays are very sensitive and reliable devices that provide fast protection against phase-to-phase and phase-to-earth faults in low-voltage and high-voltage motors.
Reverse rotation protection relays: These are devices that detect the direction of rotation of the motor and prevent it from running in reverse. Reverse rotation can damage the motor or the load, especially in applications such as conveyor belts, pumps, or fans. Reverse rotation protection relays can use different methods to sense the rotation direction, such as:
Phase sequence detection: This method uses a voltage relay or a wattmeter relay to measure the phase sequence of the supply voltage. If the phase sequence is reversed, indicating reverse rotation, the relay trips the circuit.
Negative sequence detection: This method uses a current relay or a power relay to measure the negative sequence component of the motor current. If the negative sequence component is high, indicating reverse rotation, the relay trips the circuit.
Speed detection: This method uses a speed sensor or a tachometer to measure the speed of the motor shaft. If the speed is negative, indicating reverse rotation, the relay trips the circuit.
Conas Comhaid Cosaint Mótar a Roghnú?
Bhaineann an roghnú comhaid cosaint mhótar le go leor feidhmeanna, mar shampla:
An cineál agus an méid an mhótar
Carachtaristíochtaí agus ratings an mhótar
An cineál agus an tréimhse folachtaí is féidir leo
Na riachtanais NEC agus standair eile
Costas agus inrochtaineacht na comhaid
Tugann Article 430 an NEC rialacha agus treoracha ginearálta chun comhaid cosaint mhótar a roghnú bunaithe ar na feidhmeanna seo. Ach, is tábhachtach freisin tuilleadh eolais a lorg ón dhuine a dhéanann an t-mótar agus na comhaid.
Seo roinnt céimeanna ginearálta chun comhaid cosaint mhótar a roghnú:
Toiligh an cinnseáil full-load (FLC) an mhótar ó a nameplate nó ó NEC Table 430.250 for AC motors or Table 430.251(B) for DC motors.
Roghnaigh comhad cosaint overload atá in ann a lorg ar a laghad 115% den FLC for motors with a service factor of 1.15 or higher or with a temperature rise of 40°C or less; or 125% of the FLC for other motors. The overload protection device can be a thermal overload relay, an electronic or digital overload relay, or a differential protection relay, depending on the type and size of the motor.
Roghnaigh comhad cosaint short-circuit agus ground-fault atá in ann a lorg ar a laghad 150% den FLC for motors with a service factor of 1.15 or higher or with a temperature rise of 40°C or less; or 175% of the FLC for other motors. The short-circuit and ground-fault protection device can be a fuse or a circuit breaker, depending on the type and size of the motor.
Roghnaigh comhad cosaint reverse rotation if the motor or the load cannot tolerate reverse rotation. The reverse rotation protection device can be a phase sequence detection relay, a negative sequence detection relay, or a speed detection relay, depending on the type and size of the motor.
Roghnaigh the conductor sizes for the motor circuit according to NEC Table 310.15(B)(16) for general wiring and NEC Table 430.250 for motor branch circuits. The conductors should have an ampacity not less than 125% of the FLC for motors with a service factor of 1.15 or higher or with a temperature rise of 40°C or less; or 115% of the FLC for other motors.
Roghnaigh the appropriate devices and methods for motor control, starting, stopping, speed regulation, and communication according to the type and application of the motor.
Conclúid
Is gníomh tábhachtach é cosaint mhótar sa réimse innealtóireachta leictreach a chinntíonn sláinte agus oiriúnacht mhótar leictreach agus a gcóras. Rógnaítear comhaid cosaint mhótar bunaithe ar an cineál agus an méid an mhótar, an cineál agus an tréimhse folachtaí is féidir leo, na riachtanais NEC agus standair eile, agus costas agus inrochtaineacht na comhaid. I measc na comhaid cosaint mhótar tá fuses, circuit breakers, overload relays, differential protection relays, agus reverse rotation protection relays. Monatóireann agus a chontrollann comhaid cosaint mhótar paraiméadar mar shampla cinnseáil, voltáid, teocht, luas, agus torcas chun stop a chur leis nó laghdú a dhéanamh ar dhamáiste don t-mótar agus a chóras i gcás folachta nó staid neamhchoimeádach.
Déanaimis meas ar an gcéadléine, tá cláir maith le roinnt, más gá a scrios roghnú.
