Single Phase Voltage Controller with Phase Control using Resistive And Inductive Load

In this section, a diagram of AC voltage controller is presented. At first, the output waveform of ACVR is drawn for the resistive load which is based on the pure application of operation of the thyristor. And soon after it, the operation of it based on inductive load is described.

Summary

Things to Remember

1) If a thyristor switch is connected between ac supply and load, the power flow can be controlled by varying the rms value of ac voltage applied to the load, and this type of power circuit is known as ac voltage controller.

2) The frequency of input and output voltage remains constant.

MCQs

No MCQs found.

Subjective Questions

Q1:

Write about bronchodilators.

Type: Long Difficulty: Easy

Show/Hide Answer

Answer: <h3>Bronchodilators</h3>
 
<ol>
<li>
<h4>Ephedrine</h4>
</li>
</ol>
Ephedrine is a naturally occurring alkaloid, used in patients with reversible airways obstruction. It is given orally and has a longer duration of effect because of low efficacy and frequent side-effects, it is seldom used and it is used for temporary relief of shortness of breath, chest tightness and wheezing in bronchial asthma.
 
 
Mechanism of action:
This stimulates alpha and beta receptors and also stimulates a release of nor-adrenal from sympathetic nerve ending which causes bronchodilatation. It works by reducing swelling and constricting blood vessels in the nasal passages and widening the lung airways.
 
Preparation:
It is usually available in form of tablet and nasal drops such as:
<ul>
<li>Ephedrine tablet(15mg-30mg)</li>
<li>Ephedrine drops(0.5w/v)</li>
</ul>
 
Usual dose:
<ul>
<li>Adults: 15mg-60mg three times a day orally</li>
<li>Child: 3mg /kg/day in 3/4 divided dose(not recommended for infant under 6 month)</li>
</ul>
 
 
Indication:
<ul>
<li>Bronchodilation and</li>
<li>Nasal decongestion eg: reversible airway obstruction, COPD, asthma</li>
<li>Myasthenia gravis</li>
</ul>
 
Contraindication:
<ul>
<li>Hypersensitivity with ephedrine</li>
<li>Ischemic heart disease</li>
<li>Angina pectoris</li>
<li>Hypertension</li>
</ul>
 
Special precaution:
<ul>
<li>Arrhythmias</li>
<li>Diabetes</li>
<li>BPH</li>
<li>Porphyria</li>
</ul>
 
Adverse effect:
<ul>
<li>CNS: insomnia, dizziness, euphoria, vertigo, restlessness, tremor.</li>
<li>CVS: palpitation, tachycardia, hypertension.</li>
<li>Difficulty in micturition.</li>
<li>Miscellaneous: diaphoresis, tachyphylaxis.</li>
</ul>
 
General implication:
<ul>
<li>Monitor the vital sign time to time.</li>
<li>Advise the patients not to take medicine if he/she complains of painful micturition and retention of urine and immediately inform physician.</li>
<li>Nasal drops should not generally use for more than same time.</li>
<li>Advise the patient to take medicine after a meal.</li>
<li>Store the medicine in 20-25 degree Celsus and preserve in tightly covered and light resistance area.</li>
<li>Check the urine output in an elderly patient.</li>
</ul>
 
 
 
 
<h4>2 .Salbutamol</h4>
Salbutamol is b2 agonist stimulants,which decreases the bronchial smooth muscle tone and is effective in treating the reversible airway obstruction. It acts on 15 minutes after oral ingestion and 5 minutes after inhalation and lasts for 4\3-4 hours after inhalation and 4-6 hour after orally. It is a naturally occurring alkaloid, used in patients with reversible airways obstruction. It is given orally and has a longer duration of effect.
 
 
Mechanism of action:
This stimulates alpha and beta receptors and also stimulates a release of nor-adrenal from sympathetic nerve ending which causes bronchodilatation.
 
 
 
Usual dose:
<ul>
<li>Adults: 200mg-4000mcg three times / four times a day orally</li>
<li>Child: 200mcg TDS/QID</li>
</ul>
 
Indication:
<ul>
<li>Bronchial asthma</li>
<li>Bronchitis</li>
<li>Chronic Obstructive Pulmonary Obstructive Disease</li>
</ul>
 
 
Contraindication:
<ul>
<li>Hypersensitivity</li>
<li>Glaucoma</li>
<li>Cardiac arrhythmia</li>
<li>Shock</li>
<li>Special precaution on pregnancy and lactation</li>
<li>Thyrotoxicity</li>
</ul>
 
Adverse effect:
<ul>
<li>Palpitation</li>
<li>Headache</li>
<li>Tachycardia</li>
<li>Nausea</li>
<li>Hypotension</li>
<li>Hypokalemia</li>
<li>Anxiety</li>
<li>Fine tremor</li>
<li>Restlessness</li>
</ul>
General implication:
<ul>
<li>Monitor the vital sign timely to monitor the tachycardia</li>
<li>Advise the patients not to take the extra dose/ over preparation .</li>
<li>Explain the patient that tachycardia and tremor may occur.</li>
<li>Advice the patient if a gastrointestinal problem occurs then administer the medicine with food.</li>
<li>The mouthpiece of inhaler should be properly fit to prevent the loss of dose through an open mouth.</li>
</ul>
 
<h4>3. Terbutaline Sulphate</h4>
Terbutaline sulfate adrenergic agonist which selectively stimulates β2 receptors, producing relaxation of bronchial smooth muscles.
 
Mechanism of action:
During bronchospasm it stimulates1beta-2 adrenergic receptor, relax bronchial smooth muscles; therefore relieve bronchospasm and reduce airway resistance. It`s action are similar to the action of salbutamol.
 
Uses:
<ul>
<li>Asthma</li>
<li>Bronchitis</li>
<li>Emphysema</li>
<li>COPD</li>
<li>Bronchiectasis</li>
<li>Premature uterine contraction.</li>
</ul>
 
 
Preparation:
It is usually found in form of tablet, aerosol, and injection such as:
<ul>
<li>Terbutaline tablet:2.5mg-5mg</li>
<li>Terbutaline injection:0.5mg/ml,1mg.ml</li>
<li>Terbutaline aerosol:250 mcg</li>
</ul>
Usual dose:
<ul>
<li>Adult and children>15 years: Initially 2.5mg 3-4 times a day; Maintenance: 2.5-5mg 3 times daily.</li>
<li>Children: Initially 0.05mg/kg/dose1every 8 hourly, my increase up to 0.15mg/kg/dos.</li>
<li>Injection: 0.25mg S/C in the lateral1deltoid area; can be repeated1after 15-30 minutes. If no significant clinical improvement is noted. Do not exceed a 1ampoule dose of 0.5mg1over 4 hours.</li>
<li>Metered dose in5aler: 0.2-0.5 mg(1-2 inhalation) every 4-6 hourly.</li>
</ul>
 
Contraindication:
<ul>
<li>Hypersensitivity</li>
<li>Lactation</li>
<li>Use cautiously in hypertension</li>
<li>DM(diabetic Mellitus)</li>
<li>Impaired cardiac function</li>
<li>Preterm labour</li>
<li>Closed-angle glaucoma</li>
<li>Antepartum haemorrhage</li>
</ul>
 
Adverse effect:
<ul>
<li>Headache</li>
<li>Nausea</li>
<li>Headache</li>
<li>Heartburn</li>
<li>Tremor</li>
<li>Weakness</li>
</ul>
 
General implication:
<ul>
<li>Monitor rate, depth, rhythm , types of respiration, quality and rate of pulse and assess lung sound, oxygen saturation, a color of lip and nail etc to assess the oxygenation and tissue perfusion.</li>
<li>Do not take more than 2 inhalations at a time because excessive use may cause paradoxical bronchoconstriction.</li>
<li>Instruct the patient to rinse mouth after1 inhalations to prevent dryness.</li>
<li>Advise the patient to increase1fluid intake which helps to liquefy the secretion.</li>
<li>Monitor for an untoward side effect.</li>
</ul>
 
 
 
 
 
<h4>4. Isoprenaline</h4>
Isoprenaline is a potent adrenergic beta-receptor stimulant, which causes bronchodilatation promptly after oral inhalation and persists for up to 1 hours. It acts as a bronchodilator in the management of reversible airway obstruction. The effect of sublingual administration persists for up to 2 hours.
 
Mechanism of action:
It is a sympathomimetic that selectively acts on beta 2 receptor and thus relaxes bronchial smooth muscles. As a cardiac stimulant, it acts on β- adrenergic receptor in the heart.
 
Indication:
<ul>
<li>Cardiac asthma</li>
<li>Heart block</li>
<li>COPD</li>
<li>Bronchial asthma</li>
<li>Bronchitis</li>
</ul>
 
 
Usual dose:
<ul>
<li>IV infusion:0.5-10mg/min</li>
<li>Oral: initially 30mg every 6 hourly. Maximum 840mg daily.</li>
<li>Sublingually 20mg</li>
<li>Intramascular: 1-2mg</li>
</ul>
 
 
Contraindications:
<ul>
<li>Diabetes</li>
<li>Cardiac arrhythmia</li>
<li>Coronary artery disease</li>
</ul>
 
Adverse effect:
<ul>
<li>A headache, sweating, nausea</li>
<li>Hypotension</li>
<li>Tachycardia</li>
<li>Irregular heart beat, tremor</li>
</ul>
<ul>
<li>Cardiac arrest</li>
</ul>
 
Nursing consideration
<ul>
<li>Monitor the vital signs after administering the medicine and inform the physician if any changes occur in the patient.</li>
<li>Monitor the patient blood pressure and blood sugar at regular interval.</li>
<li>Note for any toxicity and inform physician.</li>
<li>Take the special precaution in diabetes mellitus, hypertension .</li>
</ul>
 
<h4>5. Orciprenaline</h4>
 
Mechanism of action
It is beta-adrenergic receptors agonist.it is moderately selective and it stimulates the receptors of the smooth muscles in lungs, uterus, and vasculature supplying skeletal muscles and relaxes them.
 
Indication
<ul>
<li>Bronchial asthma</li>
<li>Chronic bronchitis</li>
<li>Emphysema to relieve bronchospasm</li>
</ul>
 
Doses
<ul>
<li>Orally -10mg TDS/QID</li>
</ul>
Contraindication
<ul>
<li>Hypersensitivity</li>
<li>Cardiac arrhythmia</li>
</ul>
 
Adverse effect
<ul>
<li>Tremor</li>
<li>Nervousness</li>
<li>Dizziness</li>
<li>Weakness</li>
<li>Headache</li>
<li>Nausea</li>
<li>Tachycardia</li>
</ul>
 
Nursing consideration
<ul>
<li>It should not be used with a beta blocker.</li>
<li>Monitor vitals especially blood pressure and heart rate and inform immediately if any changes.</li>
<li>Explain the patient about tachycardia.</li>
<li>Advise the patient not to take an overdose of the medicine.</li>
</ul>
 
 
<h4>6. Adrenaline</h4>
Adrenaline is a powerful sympathomimetic neurotransmitter produced by medulla and comes under sympathomimetic drugs group. It is the drugs of choice for anaphylactic shock and severe allergic responses.
 
Mechanism of action:
It is the adrenergic agonists. It increases the accumulation of cAMP at beta-adrenergic receptors which cause the bronchodilation, cardiac and CNS stimulation. It also raises blood sugar by mobilizing glucose from the tissue. it acts on both alpha and beta receptors.
 
 
Indication:
<ul>
<li>Cardiac arrest</li>
<li>Open-angle glaucoma</li>
<li>Acute asthmatic attacks</li>
<li>To prolong local anesthetic</li>
<li>Control of hemorrhage likes epistaxis</li>
</ul>
 
Usual dose:
<ul>
<li>Adult: 0.2-0.5mg S/C or I/M repeated every 10 minutes if necessary.</li>
<li>Child : 0.01mg/kg SC/IM repeated every 5-10 minutes if necessary.</li>
</ul>
 
<ul>
<li>For cardiac arrest: adrenaline 1 in 10,000 is recommended in a dose of 10ml by central venous injection.</li>
</ul>
 
Contraindication:
<ul>
<li>Hypersensitivity to drugs and bisulphites</li>
<li>Disease: glaucoma, diabetes mellitus, pregnancy, lactation.</li>
<li>Hyperthyroidism</li>
<li>Angina pectoris</li>
</ul>
 
Special precaution:
<ul>
<li>Elderly</li>
<li>IHD</li>
<li>Hypertension</li>
<li>Hyperthyroidism</li>
<li>Diabetes mellitus</li>
</ul>
 
Adverse effect:
<ul>
<li>Restlessness</li>
<li>Tachycardia</li>
<li>Nausea, vomiting and dry mouth</li>
<li>Urinary retention</li>
<li>Pallor</li>
<li>Nervousness</li>
<li>Chest pain</li>
</ul>
 
 
General implication:
<ul>
<li>Assess the respiratory status including rate, depth, and rhythm of respiration.</li>
<li>Monitor the vials carefully.</li>
<li>Notify the doctor if any side effects are seen.</li>
<li>Use 1 or less than 1ml syringes for greater accuracy of the dose when giving in a parental route.</li>
<li>The I/V route should be used only for cardiac resuscitation; if used by this route, the drug should be well diluted and injected slowly because if fast given then ventricular fibrillation occur.</li>
<li>The medicine should be stored in tightly covered, light-resistant container.</li>
<li>Do not use brown or precipitated solution and inform the patient and visitors about the adverse effect of it including tachycardia,sweating, and anxiety.</li>
</ul>

Videos

Bronchodilators

Single Phase Voltage Controller with Phase Control using Resistive And Inductive Load

With Resistive Load

If a thyristor switch is connected between ac supply and load, the power flow can be controlled by varying the rms value of ac voltage applied to the load, and this type of power circuit is known as ac voltage controller. Figure besides shows the diagram of the single phase full wave ac voltage controller with a resistive load. During the positive cycle of the input voltage, a gate signal is provided to T₁ at delay angle α and as it is a forward biased condition, the positive voltage appears across after the load after the gate signal is provided to the gate terminal. During negative cycle of the input voltage, T₁ is reverse biased while T₂ is forward biased and when the gate signal is provided to the gate terminal of T₂, it conducts and negative cycle voltage then appears across the load.

Mathematical Calculation:

The d.c component in it is zero. A_o = 0.

For the calculation of the r.m.s value of voltage,

$$\eqalign{
& Vrms = {\mkern 1mu} \sqrt {{1 \over \pi }\int\limits_\alpha ^\pi {{{(Vm{\mkern 1mu} Sin(\omega t))}^2}} d\omega t} \cr
& \,\,\,\,\,\,\,\,\,\,\,\, = \,\sqrt {{{V_m^2{\mkern 1mu} } \over {2\pi }}\int\limits_\alpha ^\pi {(1 - Cos(2\omega t))} d\omega t} \cr
& \,\,\,\,\,\,\,\,\,\,\,\, = \,\sqrt {{{V_m^2{\mkern 1mu} } \over {2\pi }}\left[ {\omega t - {{Sin(2\omega t)} \over 2}} \right]_\alpha ^\pi } \cr
& \,\,\,\,\,\,\,\,\,\,\,\, = \,\sqrt {{{V_m^2{\mkern 1mu} } \over {2\pi }}\left[ {\pi - \alpha + {{Sin(2\alpha )} \over 2}} \right]_\alpha ^\pi } \cr} $$

For α = 90 degree, V_rms = Vm/2

For α = 180 degree, V_rms = 0

The fourier component of V_o is given by:

$$V0 = {{A0} \over 2} + \sum\limits_{n = 1}^\infty {(AnCos(n\omega t) + } BnSin(n\omega t))$$

Now for the An component$$An = {1 \over \pi }\int\limits_\alpha ^\pi {{\rm{Vm}}} \;Sin(\omega t)\;Cos(n\omega t)\;d(\omega t) + {1 \over \pi }\int\limits_{\alpha + \pi }^{2\pi } {{\rm{Vm}}} \;Sin(\omega t)\;Cos(n\omega t)\;d(\omega t)$$

Solving for the value of An we get the following expression,

$$An = {{{\rm{Vm}}} \over \pi }\left[ {{{Cos(1 - n)\omega t} \over {2(1 - n)}} - {{Cos(1 + n)\omega t} \over {2(1 + n)}}} \right]_\alpha ^\pi + {{{\rm{Vm}}} \over \pi }\left[ {{{Cos(1 - n)\omega t} \over {2(1 - n)}} - {{Cos(1 + n)\omega t} \over {2(1 - n)}}} \right]_{\pi + \,\alpha }^{2\pi }\;for\;n \ne 1$$

For the Bn Component$$Bn = {1 \over \pi }\int\limits_\alpha ^\pi {{\rm{Vm}}} \;Sin(\omega t)\;Sin(n\omega t)\;d(\omega t) + {1 \over {2\pi }}\int\limits_{\alpha + \pi }^{2\pi } {{\rm{Vm}}} \;Sin(\omega t)\;Sin(n\omega t)\;d(\omega t)$$

Solving for the value of B_n, we get

$$Bn = {{{\rm{Vm}}} \over \pi }\left[ {{{Sin(1 - n)\omega t} \over {2(1 - n)}} - {{Sin(1 + n)\omega t} \over {2(1 + n)}}} \right]_\alpha ^\pi + {{{\rm{Vm}}} \over \pi }\left[ {{{Sin(1 - n)\omega t} \over {2(1 - n)}} - {{Sin(1 + n)\omega t} \over {2(1 + n)}}} \right]_{\pi + \,\alpha }^{2\pi }\;for\;n \ne 1$$

With Inductive Load

The figure below shows the diagram of the single phase full wave ac voltage controller with an inductive load. During the positive cycle of the input voltage, a gate signal is provided to T₁ at delay angle α and as it is a forward biased condition, the positive voltage appears across after the load after the gate signal is provided to the gate terminal .Due to inductive load, the current i_T1willn’t fall to zero at wt =π, it will continue to conduct until i_T1falls to zero at wt = B. During negative cycle of input voltage, T₁ is reverse biased while T₂ is forward biased and when gate signal is provided to the gate terminal of T₂, it conducts and negative cycle voltage then appears across the load and it conducts until i_T2= 0.

References

1) B CLASSES. AC Voltage Controllers. n.d. 16 05 2016. <http://www.bclasses.in/gate-exam-books-materials/gate-study-material-for-electrical-engineering/gate-study-material-for-power-electronics/gate-study-material-for-power-electronics-ac-voltage-controllers.html>.

Lesson

AC Voltage Controller

Subject

Electrical Engineering

Grade

Engineering

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